This, And don't forget knits.
Having overhauled my tie collection relatively recently and collected some winners and losers along the way, my first five ties for CBD or a slightly more casual variant thereof would be:
1) brown grenadine
2) burgundy wool challis or wool/silk blend
3) navy neat/Macclesfield print
4) rust ancient madder or grenadine
5) forest green wool (maybe striped)
I'd take a look at Henry Carter, Shibumi, Kent Wang, and No Man Walks Alone for ideas. There are other options that are likely equally good, but I will vouch for those I've listed. Assuming a mix of navy suits/sportcoats, gray suits, and the occasional brown or non-navy blue sportcoat, these will yield a great deal of versatility while also producing distinct looks.
Good luck and enjoy the wardrobe building!
Here's the write-up on the ET gren. I was happy with them so will probably by the staple colors from ET.
You should know that Berg and Berg will be having a sale on their ties tomorrow (I believe, 30-50% off). I don't think I can recommend them though. @jrd617 had a bad experience with them, and although I have only one grenadine from them, I'm not sure it will hold up. Neats might be a better bet.
Others, perhaps Erik (@EFV) might have more experience with them and can recommend them. The owners are nice folks.