First of all. Consider not buying the 13900k. If you must have Intel, get the 14900k instead - just released a month ago or so - there’s no good reason to buy the 13th gen even though the refresh is rather meh. The price is roughly the same.
Any Z790 board will be great, packed with fancy features and have most of the modern bells & whistles. No need to spend 600 euro - there really isn’t unless you’re going for something specific, like running a trio of 4090s and 2TB of RAM.
- MSI MPG Z790 EDGE WIFI - 400
- MSI MAG Z790 TOMAHAWK - 250
- Z790 Aorus Elite X WIFI7 - 350
You could even consider a b760 chipset for half the above price but since you’re buying a 4090 + a very power hungry top of the range Intel chip, the pricing is not that big of a concern, surely - just get a reasonable z790.
Since Intel supports both DDR4 and DDR5 memory, make sure you’re buying a DDR5 version of the Motherboard and RAM.
I am also a bit concerned about future-proofing
There’s no future for Intel upgrades. The next Intel chip will use a different socket, meaning a new motherboard - that’s why spending so much makes little sense. But you’ll be able to replace the GPU once something that can actually take advantage of PCIe 5.0 materialises. Around 2025 perhaps - but the 4090 will stay very relevant for another 3-4 years, perhaps longer. Same goes for faster storage, motherboards are ahead of time bar for the sockets. And there’s nothing you can do.