Just to add a little bit to the solid answers above:

2) It's a common mod, but I also suggest you leave it as a "trike" for now, and do the mod later, after you've flown a bit.

3) Ailerons on the left is an unusual configuration, but not unheard of. It's sometimes called "mode 3". However, it is very very rare, so I also suggest you keep the ailerons and elevator on the right stick. You'll adapt a lot faster than you think.

6) It's not uncommon to burn a quart in a weekend. Heck, I've burnt a gallon in a weekend of soild flying. And the cost by the quart is unreasonable.

7) Yes, get at least 2 spares. Same with props, min of 2 spare to start with.

8) Sort of. There is a lower limit to your airspeed (as you know), and it is noticeably higher than the max speed of your Aerobird. Also, new engines don't always run well at low speeds until they've fully "broken in". To make it easier to fly slow, you'll want a prop with a 4 or 5 pitch, max. Maximum speed depends on a lot of things. With an LT-40, and the LA .46 and a prop like a 10x7 or 9x9, you might hit 60-70mph in a dive. You'd have to work at it though, the LT-40 is a high-drag airframe. (which is good for a beginner). More realisitcly, 50mph is about tops in level flight for that plane and engine. These speeds are mostly guesswork though, it's hard to guage it well.