id go for the orion, so to answer your questions, i think these are right but correct me if im wrong

1 series 2 rst gearbox and 2l silvertop with a few tweaks for 150, (130 as standard)

2 i dont know if you want dics or not on the back but...rst has got drums aswell on the back but you can get conversion kits for disks on these cars

3 spax suspension, struts braces from omp or the likes

4 mk3 front end will fit but im unsure as to weather its the kit or full wings etc

5 rst turbo seats and dash should fit in easily enough

6 i have no idea where to get arts from though, demon tweakes may sell alot of the modification parts you need but ebay or here would be a good bet for the O.E.M. parts

7 some good restoration threads on here, and pictures aswell of orions,

hope this helps a little