z’ x U M2 r U’ L’ // FB – This looks quite good, the only thing I would do differently would be to do an F right before the last L’. That connects the DR piece to the center for the second block.
Continuing with what you did:
U M' U' M U r2 R M' U' M U R’// 1x2x2 – M’ U R’ U’ R’ U’ M’ r’ U r - In general it's a lot easier to place the DR piece first and then add the two pairs. Of course it depends on the case, but here I think it would be easier to do that.
U' M2 U' r' U' r U r' // 1x2x3 – For this case I would have done U’ M2 R’ U2 r u R’. Not much different, but saves one move.

R U2 R' U' (R U R' U') (R U R' U') R U' R' // corners – looks good.
M2 U' (M' U M') U2 (M' U M') // orient edges – Here you can get an arrow case a bit faster by doing U’ M’ U M. Also at the end if you did an M instead of an M’, or a U’ instead of a U, then the UL/UR edges would be lined up a bit nicer for the next step.
M2 U (M' U2 M') U M2 U' // UL/ UR
M' U2 M' U2 M2
You really seem to have the paring with the M slice down pretty well, which is normally one of the harder things for people to grasp. If you just keep playing around with Roux and trying new things, then it won't be long before you start finding easier/faster ways of doing things. Good luck!