Hi folks, thanks for the replies.
I went back this morning and tried the same process on the top of the model, and thankfully have had better success. I'm wondering perhaps I didn't get a thick enough coat of varnish, or perhaps it hadn't set properly before I attacked it with the washes etc. It was also extremely hot and humid yesterday, which might have affected the drying time on the varnish. I gave the top side a good spray and left it overnight to cure properly, seems to have done the trick.
Also noted not to bother using a satin varnish in future for this (will use gloss). I saw one chap use it and recommended over gloss as he preferred how the washes ran on it. For me however, it meant that I had to "paint" the wash over the panel lines, instead of pin washing and having the wash flow where it needed to. It looks a bit messy, but I got the panel lines to pop a little without the paint peeling off. So lesson learnt for future kits.
I'm feeling like I might let this one be for now. I've had two propellor blades fall off, repaired and then fall off again (plus a wheel lol). I enjoyed the build so much that I didn't really consider how much of a pain it would be during the painting stage without damaging these fragile parts. Perhaps I'll come back to it in a while and try to strip and repaint, I've had quite a bit of frustration with this model so I might be better for coming back to it after enjoying something else for a few days.
The good news is my next kit is a jet, so no propellors to be found :). It's an Academy MiG-23S "Flogger" in 1:72 scale. It's a very basic kit to put together, with a nice mono-tone camouflage scheme. Ideal for practicing my brush painting technique, I remember building a Flogger with my dad when I was about 6 so it'll be a nice trip down memory lane! I can't attest to the paint scheme we did for that one being quite historical however lol.
In relation to the colour of the gear assembly, you're mostly correct. However I was just following the scheme on the box, which was white and possibly related to this example here in this photo. It bears the same squadron emblem and paint scheme: