Glad to see someone else with this manifold!! I just bought the same one last week, and had concerns about it fitting in the E36. The seller told me it was a top-mount, which I knew was impossible. Did you get the 3" downpipe with it? What do you plan for exhaust and wastegate plumbing?
I still have to get a new turbo, likely a T3, .48AR from Ebay.
What model turbo is the Garrett you're using? Looks as big as the brand new T04E .60AR I've got already (decided that was too big for the stock compression ratio of 10.5:1).
I installed MegaSquirt 'n Spark on my 318ti last year after the stock ECU ate it. I've got it tuned pretty well now, running normally aspirated. Looks like the stock injectors are 'banked out' at near 80% duty cycle on the stock motor/fuel pressure at WOT, so I plan to add a rising rate FPR to supply the extra pressure when the turbo gets installed. Of course, I'll be able to tweak the fuel map to fine tune the AFR and use the LC-1 WBo2 system for automatic feedback and tuning, so the problems inherent with using RRFPR's alone won't be a factor.
Best of luck, and I'll be watching your thread carefully.
Cheers,
Scott