Welcome to the board.....I am far from an expert, but I have made a good number of tshirt quilts and here are my thoughts. I would be afraid to do a tshirt quilt by hand, but that is just me
1 - use interfacing for a tshirt quilt. While I completely understand being broke, you don't want to be sorry later. Somethings are worth spending the money on. Check on Amazon for pricing this is what I have used several times.
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
2 - I would stick to the recommendations on the batting, but that doesn't mean something dramatic will happen if you don't. I would expect that possible the batting would shift around if you quilt farther apart than what is expected.
3 - I just use the standard straight stitch on my Janome. Nothing special at all
4 - I am assuming that you would use the bias tape for binding? I make my own binding. Cut 2-1/2" strips and iron in half. That is what I would recommend you do as well - but again it won't be earth shattering if you don't
5 - as far as how much binding you need - add the 4 sides up (3 yard + 3 yard + 2.5 yard + 2.5 yards then I would add in some extra just to be safe)
As far as needles, I am far from an expert.. but I don't get too picky either. I have used something like these
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
Here is a video that may help you out
https://www.youtube.com/watch?v=JE3jqR2N4KA&t=74s
Good luck and have fun!! share pictures when you are done we all love to see eachothers projects