Help choosing TWversion 2 Mod

[Ra-az]

Hi all,
I spend the last two months getting to grips with basics of modding modelling etc.

I want to start building my mod now.

My main question:

Which TW version should I mod, Rome TW or BI TW?

Two things to keep in mind:

1) I want to use the bucellari (BI) model as a base for most of my models.
2) I would like to use (and modify) the Senate(not as a playable faction) and its allies(RTW).

So additional questions:
- Can I transfer this BI unit to RTW?
- Can I transfer the senate stuff to BI?

Any feedback would be greatly appreciated (as always)!