bass traps..which wall first

Behind the speakers first.

Yes you can use different sizes for the front and back.

Behind the speaker,in the corners, I prefer something soft and wideband. Then, behind the listener, membrane traps for deeper bass. Both can be combined if you're going DIY.

The first corner reflections would be from the corner closest to the speakers, obviously enough. So the front corners should be treated first.

Using different size traps allows you to trap different frequencies so that's not a bad idea. It would be good to determine what your problem frequencies are likely to be first, then choose a trap size for that frequency.

what are your thoughts on accoustical solutions traps up front (the 4' tall foam ones) and Aurelen Lenrd bass traps in rear (2' tall)