Beautiful "clean" car.
Looks like a keeper.
Start with battery & charging system, then work your way up - check the electrical connections to the CPS sensors. There was a post showing bad/frayed insulation of the small wires enetring the connectors due to heat cycle. Then check the negative terminal under the pass side cabin filter.
Looking for a DIY? Parts? Check this out, it might be your ticket
TMS underdrive pullies - Stewart WP - PSS9 - Beisan Vanos seals - Zimmerman cross-drilled & Akebono Euro - Deka 649 MF - 55w HID headlights - 35w HID foglights - Hualigan double din - ACS (rep) alu pedals - Euro central storage console - Breyton Magic Racing staggered wheels - M5 bumper - M5 steering wheel - Tint
Stable: e39 M54, e53 N62 & Tribby