I find your mention of the goths invading suprising. I played the WRE on vh/vh and the goths were next to useless. I think that setting just makes the huns so insane they demolish the goths entirely without contest, making them an extremely weak faction (I never saw them with more than one town or more than a full stack of soldiers, which were easily broken). I sacked two of the cities in gaul because it helped me convert them and they were too rebellious to handle, other than that I initially relied on sacking barbarian capitals to break even monetarily, until I had built up the economy enough.

I think the pointers for that faction are as follows:

-Be a Christian zealot, they have better hapiness factors
-Blitz the sedentary barbarian capitals, this removes your anti nomadic shield but gives you enough money to withstand the vandals if you fight smart.
-Build the economy and the roads necessary to defend against the huns when they come with that money.
-Believe in sarmatians, archers, bridges and night attacks.
-Don't be willing to conceed territory, so the romans gradually withdrew from the north, so what, fight smart and hang on by your teeth. Enemy factions will sack those cities and then they'll be worthless if you try to reconquer them later. Even if it seems a large city is barely breaking even remember its actually helping you alot, since it supports an entire army of troops.
-Try to use hapiness buildings more than garrisons, but remember that you need taxes so don't be afraid to use some peasants (most people find the use of peasants in any situation foreign, since RTW had its own specially intended garrison troops, no the limitanei are not their equivalent).
-Don't be afraid to break your alliance with the ERE, taking their greek cities may very well mean the difference between having three stacks of troops to fight the huns and half a stack taken unawares. Their northern cities will still serve as a barbarian shield just as well as they would otherwise.