Intel i7-9700T - good enough?

Very good I'd think. Have you considered a Ryzen with integrated graphics though, e.g. 3400G. Quite a bit cheaper and with a stronger GPU. It depends on your workload though, CPU isn't as strong.

FWIW I'm using Ryzen 2400G on Linux for Zero-K and it seems to work well with the integrated graphics.

I have I7 9700K and I used for encoding/streaming/recording. Two computers at the same time both having a similar processor. No issues as of now except the second computer that has higher temperatures because of my water cooling system.

I will always go for I7 right now but depends on what you need it for. I noticed that from an I5 to an I7 switch in this game it gave me 20% more speed. I didn't test out the new I9 but from what I saw in benchmarks on the internet there is a slight difference between it and the I7 so the extra price doesn't justify it yet.

If you want a good graphics card to solve your "fears" I suggest you go for: XFX Radeon RX 570 RS Black Edition, 8GB, 256-bit
Here is the product code that you find it on internet search: RX-570P8DFD6
I am using this video card and I have no issues with it. It's the best price mid-range video card that you can find on the market.
On Amazon, you can buy it with 175 dollars, and I bought it with 134 because of a special offer from Emag.ro.

zero-k runs like shit no matter what you use, but you won't be able to do much gaming without a dedicated GPU

Forever he's using a laptop. An eGPU setup is possible with some redneck engineering depending. thunderbolt eGPUs enclosures are too expensive, you could rip out the wifi card if it's mPCIe and slot in an mPCIe -> 16x adapter. An alternative (which is likely to work in your case) is to see if your laptop has any m.2 slots, in which case you can get m.2 -> 16x PCIe adapters. Then you need a PSU which is gonna be at least another $40, unless you got one lying around. Along with an rx 570 / 580 you're looking at maybe $200-$250 total.

This is a pretty roundabout guide: