Looking for guidance to take my imaging to the next level.

[focaldepth]

Hi all,

I have been imaging for 10 years now. So still a novice really. I am hoping for some suggestions to take my hobby forward.
My interest is galaxies and nebulae but I will point the scope at anything pretty.

I image mainly at home in urban skies. Strangely I have clouds, lots of them.

Twice a year I get to a dark sky with my smaller rig. The clouds follow me there.

I have a roll off roof Observatory (shed) with pier and am planning a roll away shed on a second pier.

My main 2 imaging setups are:

1) Quattro 10" F4 NEQ6, guided SX H18 or ZWO 1600MM
2) Quattro 8" F4 NEQ5, guided SX H18 or ZWO 1600MM
I also love my Borg 60mm F4 for wide field.

For image capture I am on Kstars/Indi/Ekos.
For processing wise I use Pixinsight with a dash of Photoshop.

I know I need to improve on the final post processing steps, a work in progress.

I have learned that in urban conditions the key is lots and lots of total exposure time.

So the questions:

If I were to throw a few thousand pounds at this where am I best spending it?.

Am I correct in thinking mount first then aperture?

If aperture what difference would 12 or 14 inch make to my images?

What difference would, say,  Orion Optics scope make over the Skywatcher.

Any suggestions welcome, reasons behind those suggestions would also be very welcome.

Thanks in advance.