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Unless it's a huge improvement, I may just opt for the single one. It would sit in the corner with a 1'x4' brick wall, 3' drywall exterior wall, and 3' cabinet surrounding it on its 3 sides. So pretty good reflection.
Secondly, been using system without sub for over a year now.

You can convince me to get two, but it'll need to be a good and technical explanation. Lol

Corner loading is not necessarily (actually rarely) the best position for a sub, output at certain frequencies yes but for the flattest possible frequency response it usually sucks. The non-instrumented way to determine the best spot is to put the sub in the listening position (playing some good sub track) and crawl around on the floor until you find the best (non-boomy) sound, it helps if you know what a good sub systems sounds like. When it sounds the best then place your sub there.

There are options to use wireless for the signal to the sub so there is no wiring. If you happen to have spare coax wiring in the walls it can be used as well.

People into audio will hear a significant improvement in most rooms with multiple subs, you may well here no difference not related to volume. Hard to say.

The problem with frequencies below the Schroeder frequency (varies room to room but my guess is about 160hz for your space) is that waves interact much differently below this frequency than above. You will have peaks and nulls throughout the room that vary in intensity so some seating positions may not even here a certain bass note while others will hear it much louder than it should be. This is based on room modes and though easy to calculate for a rectangular room more complex space like yours is harder to predict.

Honestly, most people are perfectly happy to throw a sub in the corner let their AVR do its magic to calibrate it and go on. I spend hours with a laptop/mic building an equalization curve for use in a DSP channel for each sub. In the end if your AVR doesn't have two sub outs that are independently calibrated you will not gain as much with two subs than if it did or you went the manual calibration route with a DSP. My guess is one sub will be your choice.

Rather than drone on for pages if you are interested here are two white papers on the subject of multiple subs. The first is by Welti for Harmon and the second is from Gedlee, they each have a different approach but I follow the research from Welti who worked for Floyd Toole at the National Research Council in Canada and has done much of the important small room acoustics research over the past few decades.

Harmon white paper

Gedlee on multiple subs