agree f3.2 is a bit limiting, getting everything in focus at that aperture and the aberrations from the lens itself and the dome - I see you call it a mini dome - the Zen 100mm dome? I would suggest lowering your shutter speed a little for a start, the IS in the body is very good, you will have issues with moving subjects of course, but 1/50 - 1/60 should help a little maybe 1/50 @ f4.5 ISO400 or 1/50 @ f5.6 ISO640?
I would think you could go to f5.6 probably still at the cost of corner sharpness perhaps, but better than f3.2. The full frame sensor will certainly be gathering more light but it is also more demanding , you need to go f6.3 at least to get the same depth of field as the current lens, preferably f11. So if you went f11 on the Sony, that's 3 2/3 stops over the current setting of f3.2 and assuming you do that all in ISO that's ISO5000. So the summary if I've done counting of stops correctly 1/100 f3.2 ISO400 = 1/100 f11 ISO5000. While full frame will still look better than the m43 system as you've gathered 4x the light - will it be $$$ better?
If you are technically minded then this DXO mark page allows you to compare the sensors. if you looks at the measurements ISO400 on EM-5 mkII is about equal to ISO 1600 on the SONY for Signal to noise and dynamic range: https://www.dxomark.com/Cameras/Compare/Side-by-side/Olympus-OM-D-E-M5-Mark-II-versus-Olympus-OM-D-E-M1-Mark-II-versus-Sony-A7R-IV___1006_1136_1326
I also noted you are using the Canon lens (8-15 fisheye?) at f3.2 ? I'm assuming this is with the speedbooster ? The speedbooster might be good but you're adding the aberration from the booster to the abberation from the lens near wide open to the issues with a small dome shot at wide aperture and pasting noise over the top of it all. It doesn't seem ideal to me.
An alternative you might consider is the WWL-1 it's specialty is shooting at wider apertures - it allows use of the either the 14-42 lenses or the 14mm f2.5 pancake lens and gives you a 130° field not quite fisheye but the fisheye angle of view mostly is in the extreme corners the horizontal field of view with an 8mm fisheye is about 130° while the WWL will be about 115°. I would think you could shoot that combo at f4 or maybe stopped down just a little more and just touch up the ISO a little - maybe 1/60 f4 ISO400? You can upgrade the WWL-1 to Sony full frame (or other options??) at a later date, there's been some posts on that here recently.
Having said all of that 30 x 40 inches is a stretch for any m43 sensor - it can be done but you are pushing things - the 20 MP EM1 mkII is 5188 x 3888 pixels and at 30" x 40" is 129 dpi - you can resample within reason but the starting material needs to be very good and the file carefully prepared to get the most out of it - just dropping the file into the print shop almost certainly is not giving you the best that can be obtained from the file. If you are using 30x40 paper then a 1.5" border all round is 36x27 and 144 dpi which is geeting into printable territory natively. other tricks include selective sharpening on main subject only and selective background noise reduction as well as careful sharpening techniques to avoid enhancing noise. This is the definitive sharpening guide IMO : https://manualzz.com/doc/17987997/image-sharpening-make-it-really-sharp-jeff-schewe It's old but still perfectly valid and can be done with standard PS.
All this is centered around natural light - with strobes just turn up the power and shoot at f8-11 and keep the ISO down.