@a91what will chime in shortly. From what I see it isn't complicated to control everything with a expansion board and MS2. The best would probably be the PimpXS its based on MS3 and can control a whole bunch of stuff.
You say budget. The QH uses the stock ECU. These things are getting old and the components on the computer boards are beginning to fail more and more. If you get a PimpXS you won't need another system. It can transfer to any make and model. It'll run just about anything.
the i/o is limited, I have low budget solutions for that as well... I will be releasing my own expansion module soon, adds 9 sensor inputs - 4 digital inputs [can be ground or 12v] 2pwm outputs capable of driving a boost controller
Looks like the micro will operate the AC except for turning off under full throttle. But they make a kit that will remedy that.
"If you have an MS2, you can use the two stepper IAC outputs to drive the relays – just wire the two IAC1 wires across the coil of the low speed fan relay, and the IAC2 wires across the coil of the high speed fan relay. The ECU did not control the fans on ’93 and earlier models.
Air conditioning: The ECU can turn the A/C off at full throttle, but it does not turn the A/C on. You can use an MK-RelayCtrl if you want to add this function, but the A/C can operate on its own with no intervention from the ECU. It just won’t shut off at full throttle."
The micro only has 2 remaining outputs that can be used to drive a relay, It has 3 available but WLED is used to fire the coil with a micro. The fans can be controlled with ALED and the TACH ouput. This leaves you no outputs to use for the boost controller, ALED is capable to drive this load. The AC will function but no wot switch, this is important. on the MS3 varient stinger I would just write a loop function but that cant be done on MS2 firmware. The AC relay can be altered that will allow the micro to control the AC full time, you will need an input for the AC switch. This is usually a 12v+ input circuit, this can be wired into the nitrous input as it can accept 12v+
bottom line is your out of outputs.