Stage left for me, assuming the drummer is right handed. Makes it easier to maintain eye contact with him - drummers tend to face a little towards the snare/hat.
Visually, it doesn't matter. The rhythm section is behind the vocalist, guitar and keys players
I had the same issue - dead spot at the 5th/6th fret on the G - on a P bass. I found the problem was a high fret above the octave. I think it was the 14th. The string was just touching it. It wasn't sufficient to cause a buzz, but it did deaden and prevent it sustaining. So the high fret needn't be the one where the dead spot is. The relief of the neck may mean the string is making contact with a fret away from the troublesome note.
Were you interested in or enthusiastic about what he was trying to teach? Most teachers are more than happy to help anyone who's keen but finding it difficult. It's easy to blame teachers.
They go for little to nothing. A pal has a couple that he's advertised at silly prices with no interest. He even tried "free if you take it away" with no luck. They're great, but you can get 95% of the sound from something that fits in your pocket.
The best way to deal with those kinds of nerves is to remember you are not the focus of attention. It would be different if you were a soloist, but you are very much in a supporting role and most people will hardly notice what you do. And as others say, you won't be the worst bassist in the building.
One good quality powered sub will be better than two not-so-good ones. You need clarity and not that horrible one note bass boom you get from cheap subs. You don't need stereo low end. It's pointless to have it as lower frequencies are not directional. You can also end up with oddities due to room acoustics if you place two subs apart from each other. Placement of a sub is important, so worth experimenting. You should be able to send a line level signal from your Midas to an active sub (or subs).