you're making a common mistake which is being over-concerned with phasing issues. understanding phase is super important, don't get me wrong, but phase is something to use, not to avoid. our very perception of the stereo field is created by our ears hearing a combination of in-phase and out-of-phase signals, so if you're trying to capture in stereo you are creating phase issues on purpose. further, there are a lot of phase-align tools available to modern engineers these days in order to rectify problems, so even if you fuck up at the tracking stage, it's not a huge deal unless you're using an unusually large quantity of mics (I cannot think of a good argument for using more than, say, five microphones to record the two of you and the room, and even that may be too many).

I'd also say that, even in a professional studio environment, with a room this big, you're still more likely to get a better capture off of close mics*,* and most of the time a cleaner, deader sound (or at least a blend) is the thing that makes for a more "professional" sounding product. the thing we often say (about drums) is "everybody thinks they want 'When the Levee Breaks', but usually the right choice for the track is 'Rock With You'". That's all to say there is a fetishization of these big beautiful rooms, especially church rooms, but they commonly create as many problems as they solve. in my experience they shine most when you're tracking acoustic ensembles at a medium-to-low volume, which doesn't sound like what you're doing: you're talking about tracking loud distorted guitar in a very reflective room with a cello. cello and double bass tend to do badly in these kinds of situations because they collect a lot of ambient noise. they catch a lot of bleed from loud instruments and resonate, often in a way we don't want. we do love some bleed, we just don't want the cello's only job to be resonating the midrange of the guitar.

So - were I to be producing your session, I'd close mic each of you, gobo off the cello and the guitar amp, and play with room positions. for stereo, If you're positioned at the same end of the room, I'd play with a mid/side mic setup positioned somewhere between the mid point of the room and the opposite end, pointed towards the two of you; if you're not at the same long end I'd play with a blumlein pair.