The best reason to put MS on a stock engine is if you're converting from carbs, or you have a dead MPS. I'd say that in a few years, good MPSes will be so uncommon that it will be much cheaper to do MS than it would be to find a complete set of working D-Jet parts. I don't think we've quite reached that point yet, but we're close.

You can use the stock injectors, though the 2.0 injectors are pretty marginal, as they're so big that getting good idle is difficult. The problem is that with their size, you start to run into practical limits on how short the pulsewidth (the length of time the injector is open) can be. 1.7-1.8ms is pretty close to the lower limit, as the injector takes about 0.8-1.0ms to open fully, and 0.8-1.0ms to close fully. So, at the minimum, you're "open time" is 0, and you're depending on the erratic amount of fuel injected while the injector is opening and closing to supply fuel for idle. Dave Hunt got this to work, but it was a near-run thing. airsix is running smaller than 1.7 injectors (from a Subaru) on his turbo 1.7 at 1.8ms for idle. The D-Jet ECU is all analog, so it can actually do things like use a 1.755ms v. 1.756ms pulsewidth to vary idle quite easily. MS (by default) is limited to 0.1ms steps in the pulsewidth, and there's a 6% difference between 1.7ms and 1.8ms.

The 1.7 injectors actually work better with PEFI on engines up to 180hp or so. I have a 2.0 plenum, throttle body, and runners I intend to run with 1.7 injectors on a 2.2 soon, so we'll see how well it works. If I run into idle problems, I'll probably dig up some smaller injectors.

You can use the stock air temp sensor and the stock CHT with MS, which allows you to program the temp/voltage curves to match your sensors. You can't use the stock TPS, but you can get around that by using the MAPdot mode in MS, which uses changes in the MAP signal for acceleration enrichment. You can use the stock fuel pump and the stock fuel pressure regulator. Converting the regulator to use manifold pressure as the reference, rather than a fixed reference, is a very good idea. airsix posted some photos on how to do this on this board. The idea here is that manifold pressure rises as the throttle is opened, so the relative pressure between the fuel rail and the manifold goes UP near idle, and goes DOWN near WOT, which is the opposite of what you want. By referencing manifold pressure, you "flatten" the fuel curve from idle to WOT, lifting the min pulsewidth and lowering the max. This gives you more tuning latitude at these extremes.