XL guide: Volga-Bulgars

[Peasant Phill]

When blitzing or in the opening of your campaign in general, you have to be very aware of your economy. The revenue of steppe provinces are in no way comparable to the revenue of the lush West-European provinces, nor do they have the trade potential of the Mediterranean provinces. Ignore your economy in the first ten years and you'll be the weakest eastern faction for a long time. And believe me Novgorod, Kiev and Bohemia are just waiting for a chance to enlarge their territories unpunished.

This advice is even more important when blitzing the rebels. The Volga-Bulgars are Muslims and the neighboring provinces are all orthodox catholic, which means that their are more men needed to pacify the recently conquered regions. More men => more expenses.
I would advice to develope your farms and trade first before starting with your military. Also don't just garrison until you have loyalty for very high taxes, calculate if the increase in income is worth the increase in upkeep.

[Kavhan Isbul]

As far as the economy is concerned, I recommend getting to the Baltic as soon as possible. As the Volga Bulgars you cannot avoid a war with the Novgorodians, better sooner than later, as the Novgorodian units are overall more powerful because of the Vikings and the Druzhina cavalry and infantry. Novgorod is a rich province, and it allows you to build a fleet and start developing trade. It also controls Finland, and from Novgorod it is easy to expand along the Baltic, and even to conquer the Scandinavian Peninsula. The Danes and Swedes have strong infantry, but most of it cannot defend against heavy cavalry and the battles with them are easy - I would personally rate the Scandinavian factions as the easiest enemy the Volga Bulgars will face throughout the game.
An alternative option is to push south towards the Black Sea, but the Turks are likely to beat you to Georgia and the Cumans can be tough to deal with. Conquering their lands is best reserved for later, when they are in war with the Hungarians and perhaps also the Poles, Kievans or Lithuanians.
Controling the Black Sea and the Baltic will be important eventually, because once you grow relatively large, the Catholics tend to send Crusades your way and you would not want any of them to appear in an undefended coastal province.

[Peasant Phill]

As the Volga Bulgars you cannot avoid a war with the Novgorodians, better sooner than later, as the Novgorodian units are overall more powerful because of the Vikings and the Druzhina cavalry and infantry.

(Un)fortunately these words are undoubtedly true. But like Kavhan said, it's your chance to get to the baltic without upsetting to many factions.

Now, how do you go about a war with Novgorod?
On strategic level, an attack on Novgorod itself will probably mortally wound your enemy. As Novgorod is their main troop producing province.

On tactical level, the war will be somewhat harder. Again, like Kavhan said, Novgorod has some very strong units. You'll most likely face armies consisting of rus spears, vikings and boyars (maybe with woodsmen or druzhina). But some tactics can solve this problem.

tactic against vikings:
Vikings wreak havoc on your spears and in woods. They can hold their own for a while against most units. Their biggest problem is their lousy defence (normal as flankers). To cash in on that weakness, I use some fast cav against them. Chernye if possible but steppe cav is also possible. Move two units of fast cav to the back or side of the Novgorodian battleline and locate a good target. This could be a viking unit that's lagging behind or who's flanks aren't protected. Let one of your horses charge the vikings while the other unit keeps moving to position itself behind the targeted vikings. Just before your charging light cav and the counterattacking vikings collide, you should stop the charge and move your cav away ( the feint attack) and let the vikings chase you. while this happens you should position your second unit in the back of the vikings and charge them (wait long enough so the targeted unit is to far to get support). When the vikings are hit in the back, your decoy should turn again and charge the vikings to. If done right, the vikings should be charged in the back and immediately afterwards charged while reforming. The depleted viking unit will run in just a few moments. Afterwards, rinse and repeat.

Tactics against boyars.
two words: massed firepower. Use a shield wall with more missile units than the Novgorodians. Although boyars are excellent fighters (so attacking will be very costly) they are horsearchers at heart. They will missile duel instead of charging your spear wall. Don't attack them until all your arrows are depleted. Alternatively you can use horsearchers as uncatchable arrow platforms. But be aware that light cav can seriously ruin this strategy.
I like to use steppe heavies behind a spearwall. The steppe heavies have AP missiles, are armoured, mobile and can fight well if needed. If it is safe enough, you can encircle the boyar unit to minimise casualties.

Tactics against rus spears.
To be honest, I don't have a tactic against this unit. The Rus spears are probably the best spear unit in early. The Volga-Bulgars don't have a unit they can use in a rock-paper-scissor manor against spears unless you've teched up to Varangian swordsmen. I always try to keep them out of the battle until most other units are depleted or running away. After that I swarm them from all sides and hope they rout fast. if I can't keep them from fighting I try to keep them at bay with my Kursybashy and support them as soon as possible.

[Kavhan Isbul]

Initially, if the Volga Bulgars manage to get to Moscow within a turn or two and beat the Novgorodians to it, the latter have no choice but to conquer Finland and Estonia. Estonia is the worst province to hold in the entire XL mod, because it is so ridiculously rebellious that I doubt there is any point in conquerint it at all, other than for strategic purposes (if you have ships in the Baltic, you might want to prevent the Scandinavian factions from gaining a foothold on your side of the sea). Anyway, the Novgorodians have to tie up a significant number of troops in Estonia just to quell the inevitable rebellions. Novgorod is usually poorly defended, and it is easy to take, forcing the Novgorodians to flee to their castle as the AI tries to avoid a losing battle. Next, there is a tough defensive battle against them, and they tend to be allied with the Lithuanians, who show a tendency for supporting them with some more Boyars.
I prepare for this battle by building plenty of Bashkorts, as they are the only way to deal with the Druzhina infantry uber unit of the Novgorodians (and the Kievans). One or two units of Bashkorts hold the enemy, while another unit decfimates it with javelins. The Boyars create a problem, as they tend to kill quite a few Bashkorts with arrows, so you will need some archers and some Kursubays to deal with them. There will also be Vikings, and perhaps even woodsmen, but these are basicly fodder for the Bulgarian Royal Cavalry.
I also always build an Inn in Moscow as early as I can - the Volga Bulgars need it for the Cherniye Klobuki anyway (and these are a great solution to the mounted crossbowmen the Novgorodians usually train), and when I decide to invade Novgorod, I hire whatever mercenaries I can. It is hard to afford them for too long, but many of them die in that great defensive battle for Novgorod (if they do not, then they die storming the castle), and once Novgorod falls, the pillaging pays off. Novgorod itself is more valuable than Volga Bulgaria in all possible aspects - income, trainable units, strategic position.