Having finished the long English campaign on m/m here are my thoughts.

1) The best thing I ever did was to turn take the whole of the Uk and Ireland ASAP before teching the settlements up much, then converting all of it to towns and using it as a money maker. The computer will almost never go for amphibious assaults, so you can leave it poorly protected and it'll finance anything you do.

2) Iberia is the best place to assault, possible even before taking France. It's easy to defend once taken and provides a great staging area for you to head towards north africa and into the non-Catholic regions.

3) The French may hate you with a passion, but the pope never let any attack by me or the french last more than one turn before threatening excommunication. This means all French aggression towards me got thwarted and any assaults against France required a mass assault on several provinces, backed up by artillery in order to take several settlements in one go before the pope could get involved.

4) Yeoman Archers can decimate armies, especially when backed up by armoured swordsmen. Retinue archers probably aren't worth the 9600 to upgrade the facilities, but the Sherwood archers are worthy (available through the woodsmen guild, great at killing heavily armoured troops and cavalry)

5) Mounted missile troops can absolutely demolish most English armies, but the English starting position means this shouldn't be much of a problem till the very end stages of your campaign.