Seems a bit optimistic but I'd start the first third rail EMU Preservation line.
The first challenge would be finding a suitable line, and secondly staff training for working alongside an electrified line and so on. The rest would go on buying rolling stock, that depends if the 'already' owners would be fine with me buying there units.
Rolling stock: EPB 5759 (The group would still own the unit but would be able to run it) the Brighton Belle (Once restored) 3CIGs 1399, 1497, 1498. 3CEP 1198, 4BEP 7105. I would also try to buy my favorite two Networkers off the leasing company. (465248, 465914).
Just because would be electrified does not mean we wouldn't have a diesal unit/loco. Would probally buy an Cl08/09 shunter, 'Crompton' 33035 (NSE livery) and have a 'Thumper' unit to.