I sent you over here, so hopefully you get the answers you need. Or maybe they're under the search function.
As someone already mentioned Amazon JP (I have used them before and never had an issue) for newer MP releases is great. Someone like MP Inferno would be C$175 shipped to your door after conversion from JPY, where on eBay they may be C$200 plus another C$20 for shipping. At BBTS he is on sale, but with shipping and the Customs charge I always get from them, it's still more than Amazon JP.
For eBay, I have used US, JP and HK sellers (
toyspark, animeking_inc, iamratchet, etc) before without issue but I always compare the prices between them and the big online US retailers like BBTS, etc.
I have never bought MP from Canadian online retailers due to their markup.
For your 4 questions:
1) I only have the original G1 SS, so I'm not sure if the new launchers only hold the new missiles. Or if they can hold the old ones.
2) I've seen people online assembling the new WM Reissue Devy, so unless there's a QA issue, it should combine properly.
3) MP Hot Rod? I recall hearing there were issues but no clue about him. Sorry as I don't have him.
4) There is a new Megs coming... MP-36 toy version(?). For MP-36 Megs, they shouldn't have the orange plug if they're from overseas. But ordering from a US site -- they would probably have it.
