Nice engine you got there! While your issues do sound like a MAF problem (check the MAF readings via OBD!), some turbocharged Volvos are notorious for fuel pressure regulator issues. Basically the regulator diaphragm ruptures and fuel gets into the pressure regulation vacuum hose. Typically this causes poor starting (especially cold) because of an excessively rich mixture. Black smoke out of the exhaust you noticed supports this as well.
Here is a simple way to make sure that your fuel pressure regulator on your T5 is toast: after the engine has been running for a while, remove the fuel pressure regulator vacuum hose and look if it's leaking fuel from the regulator side with the engine running. The hose is on there tight with the vacuum present, you might need to turn off the engine, remove the hose, plug the engine side to prevent a vacuum leak and start it back up again. If you see fuel dripping/spitting - the regulator diaphragm is ruptured and you need a new regulator. Don't make quick conclusions if you see nothing, sometimes it takes a while for the fuel to show up. If you noticed a strong fuel smell from the hose - that is an immediate bad sign.
If you are somehow unable to carry out this simple test you could also connect a pressure gauge to the schrader valve on the fuel rail and check if the pressure maintained by the fuel pressure regulator is correct. Value should be stamped on the FPR itself or can be found online (probably around 3 bar). This value should only be true when you prime the system without starting (ignition on) or with the FPR vacuum hose disconnected, otherwise pressure will be altered by vacuum/boost. If the pressure is completely wrong, your FPR is probably dead. Unless your pump is in a horrible condition, but I'd say it's much less likely.