There's a bit of "it depends" stuff here, based on what you use & how much you use it.
Generally speaking, if you use both inventory & patch items, you will be looking at roughly 5-10 MB of data per client node. So for 8,000 clients, expect a worst case scenario of 80 GB on the DB-server.
<This CAN go quite a bit one way or another - for instance, if you were to turn auditing on for "everything" & never clear that out, your database is going to balloon something horrifically>.
For 8k clients, 16 GB of memory "may" be enough, but you may want to keep an option open (prep-wise) to give you more. Again, there's some "it depends" factors here. I've seen people with 10k clients hammer a Core into the ground that'd usually serve 100k clients just fine, just because they decided on certain odd config items (full vulnerability scan & full inventory scan, every hour from every client).
So - again - this can go either way depending on how you go about configuring key items.
Your primary CPU / Memory munchers are going to be IIS (as a lot of stuff is based on www-services) and the Inventory service (not so much on memory, but will munch a lot of I/O).
Fast disk I/O (both on the Core & the DB-server) is a good idea, as is having a DBA that maintains your database (regular maintenance, at least 1x full re-index per week). There's various articles on things to get right here:
... so as basic recommendations go, the above can work fine. I can happily draw on past experience where certain customer configs would annihilate such a Core setup (purely because of how they configured things).
So you CAN paint yourself into a corner. If you're doing this "alone", I'd strongly advise you to get in touch with a partner to keep you from configuring yourself into trouble. Much like the way to hell's paving, "problems" often come from apparently good intentions .
I hope the above makes it clear that its very much not JUST a question of "hey, I want to manage 8k clients", but a much more in-depth discussion of:
- Here's what I want/need to do.
- Here's how often I need to do it
- Here's how my org is spread out geographically / across time zones
- Here's other political / legal stuff to be concsidered.