That car will be 'Post Vintage' in 3.5 yrs approx. IMO it would take that time to go from a DD to a show winner, as a rolling restoration. Drive and enjoy it - Join a club and show it - Some BMW Clubs run track days (see how good you really are!). Cruise it - but please don't make it into a rice grinder clone.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i