That is a pretty awesome collection of classic consoles to part with. Are you sure its worth upgrading to the X when the next generation is only 2 years away? Thats been the thing holding me back, spedning 500 plus tax just to have the system be obsolete so quickly.
It's worth it to me personally. I spend a lot of time gaming and probably 80% or more of that is on Xbox. I'm by far the most invested in the Xbox ecosystem between the domination they had last generation and the pro-consumer practices of now, like BC, among a bunch of other reasons. I pretty much only play multiplatform games on Xbox unless I get something for dirt cheap elsewhere, or want it on the go for Switch. Finally, I generally wait at least a year to upgrade to the next generation of consoles, so I think I'll be fine there. If all these studio acquisitions pay off and MS can actually give me a reason to want to upgrade sooner then it's win/win I guess.
As far as the retro stuff, the majority of stuff I'm going to trade/sell is ancient stuff I have little to no affection for personally. The consoles pre-NES are just not that interesting to me, and have been sitting in a closet for like 10 years. Any Nintendo related stuff I'm taking in tomorrow (N64 and Ocarina so far) is stuff that I have multiple of so won't actually be without. Finally I'm getting rid of most of my Genesis and possibly Game Gear stuff. With Genesis I have access to everything I care about on modern systems, and Game Gear is beyond cumbersome in the modern age. As I've gotten older I've gotten less attached to the hundreds of cartridges that rarely get touched in my house, so I've slowly been pairing back to just my most fond games for the two main consoles from my childhood, SNES and N64, along with other Nintendo stuff mostly. As far as building up a new collection, I've actually switched to more recent consoles in the past year. I've gained more interest in PS2, Xbox, Gamecube, and Wii. I think I've just played enough of the older stuff to the point that I'm fine with emulating it if I really get the itch.
Lastly, the heavy blow is softened a bit by the bonus $60 game and PUBG code I can gift or sell.