Compatibility questions

1) No problem, sanded or not. Mr Surfacer gives a pretty silky smooth finish - you may not have to sand. I have used the combination numerous times without issue

2) ?

3) ?

1 ??? but probably ok, better leave that to someone that uses that combination though.

2 If the paint is dry and fully cured (like a couple of days) it really shouldn't matter for a simple wash. If you are talking about some of the more vigerous weathering techniques like dot filters, I've seen several who recommend using opposites (oil over acrylic, acrylic over enamel) so the thinners used to damage the underlying paint.

3 Once fully cured acrylics and enamels seem to be mostly compatable, I think its the laquers that lead to problems when used with enamels.

As with most things if in doubt try the combination on something that doesn't matter, discarded plastic is great for this (old for sale signs, plastic packaging etc)

vaw1975

When that's finished, what can be sprayed over that? I read someone used Humbrol clear matt coat (in the Me 410 build thread of chukw I think).  What about Tamiya Flat Clear?

Tamiya's Flat Clear spray (TS-80) is lacquer based, so apply in very light mist coats and allow to dry between coats.

If you are talking about a bottled product X-21 Flat Base, be aware that this is an additive to make gloss paints flat, and isn't a clear flat in its own right and should not be used on its own.