There's very little extra room in this build

For standoffs you can go with the 17mm standoffs from the standard SlamNasty or if you are like me and bought the SuperSlamNasty you'll need taller standoffs. If you can find 16mm that would be perfect, but i wanted color to make it easier to find in a tree and all i could find was 15mm so I added 2 .3mm washers under each standoff. This gives about 2mm from the top of the nuts on the standoffs to the air unit. The air unit does touch against the JST connector on the FC but not hard if you want to avoid this use the 17mm standoffs or another washer.

For mounting hardware I just used M3 button head screws from the bottom plate (whatever i had on hand) and the provided gummies that came with the flight controller and some 2mm ID o-rings.

The air unit itself is mounted upside down with VHB to the underside of the top plate. no issues with heat.

Last if you need a receiver like me i just took an XM+, heat shrinked it stuck it under the camera with more VHB.

I run 4S and LOVE the T-Motor T5150 props because they're so punchy and insanely durable. At first i had some ZMX 2550kv motors however they were killing my batteries. I could only get about 2:15 and that's with good batteries so I needed to either prop down or motor down. At first I propped down to HQ 5x4.6x3 1S which are great, just not durable. wanting to keep using the T-Motor props i swapped out for the EMAX red bottoms as they're 2300kv. Much better but still beed some tuning. I'm still looking for "new" low kv (for 4S) motors as a replacement. suggestions welcome in the ~2300kv range.