1. ECM, or ECU is a stock one, that is Bosch ME2.8. You just unplug the old engine, throw in 3.7 one, plug in and start. ECU recognizes bigger displacement and adjusts all the stuff on it's own.
2. Next mods will be related to engine and drivetrain mainly. Suspension and visual details can wait for now. Brakes will be refreshed (steel fluid lines, sport brake fluid, ceramic pads, drilled and slotted rotors) but within factory spec. Better tires of course, spacers on front and rear, as I want to stay with stock rims.

I already bought AMG fuel pump (found new one at 50% sale) and new filter, they just sit here and wait for a spare time to install:

Fuel pump code: 7.00228.51.0

First I plan on fitting DCAI, bigger throttle, and bigger exhaust manifolds - I will have a shopping spree at Needswings lol.

Second, I will get engine heads reworked. Already bought spare heads for 3.7 in good condition from scrapyard for like 300$ total, they already wait in my basement. I have custom cam and head manufacturer/workshop in my city, so I will get them to build new cams, port heads, change valves (propably bigger intake ones) and springs. My plan is to increase effective max RPM from 6,200 to 7,200, not only for pure power gain related reasons, but also wider powerband will make 1st and 2nd gear much more usable. Also, intake manifold could be rebuild with solely short runners - most propably HP increase would by far outweight the low-end torque drop - idea will need further discussion.

Third, lightweight flywheel, sport clutch and wavetrack - propably the most expensive step, as I will have to source all the stuff from third-party, expensive foreign sellers.

Fourth, got some reasonably priced heavy-machining shops in my area, so lightened crankshaft and knife-edged, forged conrods and propably pistons - got some ideas in my head about increasing CR to 12-12,5:1, everybody's so occupied with increasing boost no one tried that in NA M112 lol.
There is also that thing with stroker cams for M112, made by Brabus for 3,8 engine, but I doubt i will be able to find just a crank for sale anywhere - it would make it effectively a 4.0 engine - will see about that when the right time comes - the only two sure things are, I stay manual and naturally aspirated.