I would not worry about the coma till you give the scope a try as see if it really bugs you. I am changing to more premium eyepieces after quite a while but I have been able to cope with the coma even in my 13" which is f4.5, it has not been nice but at least I could use it.
The ripple in the tube would be a baffle which is not necessary for your 10". To try and increase contrast some people flock their tubes, others set up baffles and others do both its your choice. It is more important in areas of light pollution.
I would recommend you use your scope as it is for a while before you start any mods or accessory purchases except for some collimation tools.
Keep looking up
