I've been had fun playing as Rhaegar too, having reconquered much of Westeros through forced vassalization - it's the only way in which you can blitz-conquer without racking up immense infamy, which is quite realistic and historical. Most hilarious thing that happened, though, was that Eddard Stark and Catelyn had a falling-out, being rivals and fighting a few wars
If you still take suggestions on alternative start dates, I'd throw in a vote for the start of the War of the Five Kings.
The latest word on the CK2 forum is that it will have Emperor-level titles that are actually able to have kings as vassals. Which should make it possible to have the King of Andals, Rhoynar and First Men as a direct overlord of a king of one of the seven kingdoms. It annoyed me to no small extent that I couldn't impose vassalage on the kings, I had to seize their crowns and force them to essentially become dukes. Frankly, if I had done the mod, I would simply have defined all of Westeros as one kingdom, and the seven realms as mega-duchies. In the books, pretty much all noble houses that are mentioned are under direct vassalage to the ruler of the realm anyway. Knights with large enough lands to be vassals in their own right, like Ser Gregor Clegane, would probably not be big enough to even count as counts, in CK terms. After all, we accept in vanilla CK that there are tiers of nobility below counts, that they're just not shown for simplicity.
Fantastic work nevertheless. If I didn't have my own mod (VRRP for Victoria 2) to occupy me, I'd offer to be your bannerman. However, do you have plans of making the Westeros mod for CK2 when it comes out? Since it's at least a year until then, I might be less occupied with VRRP by then, and might well have the time to take part in CK2 Westeros mod.