The biggest challenge with BGAs from a hobbyist perspective isn't the soldering. There are lots of hobbyists successfully reflowing BGAs with toaster ovens. The bigger problem is manufacturing the PCBs to break out the BGA balls. TI has some BGAs with a proprietary ball pattern that are designed to be broken out with just 4 layers, but that's the exception, and you generally need very narrow traces and trace clearance to route between balls and vias. I just looked at OSH Park's current capabilities and they only do up to 4 layers and their DRC specifies 6 mm minimum trace width and 6 mm minimum spacing. I've heard of people using OSH Park and similar lower-end prototyping services to manufacture one-off PCBs for fine-pitch BGAs, but you'll be failing DRC by a massive margin, so expect terrible yield on the PCBs, assuming any of them work at all.
Unfortunately I think DRC will be similarly challenging for most SoM connectors since their pin spacing has a similar pitch to BGAs, so you'll probably need an off-the-shelf break-out board to work around that. Honestly, at some point you should consider whether a vanilla dev board with low-speed GPIO headers could meet your requirements.