A few lessons learnt from tinkering with my TM MP7:
If you want to use propane and its shooting too hot, you can buy a pack of these as replacement rocket valve springs to cut them down to size to get the fps you are looking for: https://www.amazon.co.uk/dp/B076M27VH2 much cheaper and easier to source than buying individual originals from TM.
Changing from stock to a Laylax purple hop rubber and 6.03 barrel somehow lowered my fps when the hop was set for .25s. I assume this is because the hop rubber is softer.
With a T2 + unity high mount clone you can get a decent cheek-weld and sight picture even with a full mask like a empire EVS.
I found overfilling the mags with bbs causes the the mag to put pressure on the nozzle and not feed the first round - this could just be a tolerance with my gun though.
Changing the barrel sucked, I kept knocking the trigger bar out and I wish to never do it again.
I was going to put a silicon ML hop rubber in my MP7 but after seeing so many bad reports I left it out and went with the Laylax purple one instead.
Also red dot recommendations: Vortex Crossfire is good and you can get custom protectors for it on ebay from red_dot_engineering