Firstly Kudos for actually working on your own art and with using tools not really designed for the job. Personally though I would probably use something like Gimp on the basis that you have found all the artwork already.
Unfortunately there doesn't seem to be any structure to the marquee. Everyone is just sort of floating in space. , I would draw an imaginary line and move everybodys feet onto that line, It doesn't have to be a straight line either it could be curved. Pacman down to same level as DK, Spaceships up to top right top left facing as if attacking the main characters, The little dig dug guy down and center, Frogger down and swap places with Qbert. Tapper should be in front of other characters. Lose the space invader entirely the art style doesn't really fit in properly. Arkanoid paddle and ball I would move to right and below DK.
I would find a more arcadey font for the name. Also may be worth thinking about changing the name, I kind of regret calling mine doctonicade. It's bloody obvious it's an arcade and I know it's mine
As for the control panel, no issues with the layout, although is the spinner location actually comfortable to use, do you want it centered for aesthetic purposes? What about coin buttons or are you going to have them on front/coin door etc.
Artwise it looks completely disjointed from the marquee, I would reuse the marquee elements in some way, It's just a little to plain and simple. Maybe smaller pacman and ghost but with pellets between.
Hope this has helped a little bit.