For question # 1, try using
Multi mode. With this mode, you can layer/split up to 16 parts on the keyboard and also on several MIDI channels.
About question # 2, you'll have to recreate those Programs/Performances. This will require effort and it even may be impossible for certain features... you'll have to find out
Regarding question # 3, if you'll commonly use the Multi mode
with many layered complex Programs, you may be safer with TI2. Otherwise, I think TI will be just enough. Until now (this also applies to the new OS5), every OS update will equally be applied to TI and TI2