appropriate for 10 year old boy?

When I get an expansion, I like to go though to cards and pull out the 2 or 3 that end up being too much for my younger kids. My 9 year old doesn't need to see the picture of the "Ether Bunny" getting high. Otherwise, for the most, it's fine. Keep in mind, it is a game of backstabbing your friends to get ahead, albeit in a humorous way. I have 4 boys, 9, 10, 16, and 17 and we all love it and they invite their friends. Little guys have no problem understanding it. I just realized how long winded this was, sorry. :)

Can this be played with only two players? The other editions are 2 to 6 players.

Yes, but as with all munchkin gams is better. I would reccommend playing with a group of 4-5 but 2 is doable. It may be more tricky though.

Is this Munchkin rendition able to be used in the overall game or should this/must this be played alone with like theme?

As far I understand it... ALL Munchkin games can be mixed together OR played as stand alone games. There is even a Post-Apocalyptic version now too.

Can this version be mixed with the original version, or is it better off as a stand-alone?

Each set can be mix and matched as you like. That said, each of them has its own mechanics which can be an odd fit with the others. This one deals with Portals and Cultists which both are rather important, but not represented in other sets.