The parts

Here is what I planned, and what I got.

Motherboard: Asus ROG Strix Z390-E

    Pretty much planned and got. Has two M2 sockets, is Z390, should give me some breathing space in future.

CPU: 

    Planned a better core i3. 

    Changed: to a Pentium Gold (2 cores, but 4 threads).

    Got: Core i5-9600K (that gives me some overclock possibility. And i think it will be years before anything better comes down in price significantly. So it should be okay for a good few years.)

CPU Cooler:
    Planned: A big ole Noctua cooler, because i think they look cool :)
    Got: A CoolerMaster ML240 AIO. I'm always worried that big cpu coolers will fall off! Plus, I've never had a watercooled machine before, and the AIO was stupid cheap. Plus it's got RGBY'all
    (Note - if we get what we pay for, I'd best watch those temps, and keep an eye out for leaks).

GPU:

    Planned: Two Zotac 1060s.

    Changed: One Zotac 1060 (get a second in the future, when i have everything running, and they are maybe cheaper.

    Got: Zotac 1070. I worried about upgrading the 1060 later, and the 1070 wan't much more.

Memory:
    Planned: 16GB
    Got: 32GB. I didn't want to get two 8GB sticks (if I'm going to max the memory in a year, I don't want to be wasting DIMMS). One 16GB stick just seemed wrong. So 32 in 2*16. NOTE - I got 2666MHZ memory, but it reports as 2111MHZ (or something). It looks like all DDR4 apparently runs at that speed. I needed to go in to my bios and over-ride it.  I did that and it all seems stable. Assuming it did actually work - I should check.

Disks:
   Got what i planned for.
    M2 NVMe (PCIE) 250GB. Stupid fast, to run Ubuntu from
    M2 SSD: 500GB. May as well use the slot. To install Win10
    SSD 1TB: A nice bit of reasonably fast shared storage.
    HDD: 3TB 7200. I would have gone 5400, I don't want to use it much. But the 7200 was only about £5 more. This gives me a big chunk of space to store big files / rarely used files and similar. (And a few weeks later - i rarely hear it spin up, well, I've never heard it spin up - but it does get used. If i need significantly more space I'd get another one as far as noise is concerned.)

Power:
    Be Quiet! 750w Straight power. (planned, got). It's efficient, enough power, quiet.

Case:
    Planned: Pretty much every case in production.
    Got: Be Quiet Silent Base 801. I'm not likely to be pushing thermals too much, so a quiet case seemed a reasonable idea. It's big and spacious, has a glass side (RGBY'all)
    Wish I'd got, maybe: Lian Li PC 011. I saw a review of this once I'd bought the BQ 801. if i'd seen that before, I'd have probably got it. I actually love their sit/stand table PC case too :) But that price...
    Want to get: I actually want to build a case from scratch at some point. Pipe dreams.
    (A few weeks later - I like this case - so far no heat issues, and it is lovely and quiet, which counts as it sits beside me on my desk.)

Others:
Keyboard: Drevo Tyrfing v2. I got blue switches by accident. Don't get blue switches if you're an aggressive typist. I like it, plus RGBY'all bling. It's pretty.
(A few weeks later - I like this keyboard. But I'd definitely get quiet switches in future. This is loud as a loud thing.)

Second monitor. I'm used to Laptop + monitor (screen and small screen), or dual (or more) monitors at work. I got a flimsy cheap AOC 22" monitor as a second screen. (Two weeks later - the AOC works, but is a bit of a '57 chevy, as it were. To be honest I should have just bought a widescreen, there are some for not that much more than this thing, and a monitor stand for my old viewsonic to hold it in portrait mode - possibly an upgrade before end of year.)

Building it: Maybe the subject of another post. I wish I'd taken pics at various points. I haven't built a PC for around 16 years, but it all seemed to go quite well. Took me way longer than it should, and my cable management leaves a lot to be desired.

Some notes i did make on pc parts picker:
Everything went together fairly easily. I haven't built a PC for well over 15 years, so it's not like i have recent experience :)

The CM AIO was a bit of a bugger - getting that back plate to stay in place while I screwed the front on was a right pain. I ended up using a piece of foam from one of the packages to hold it against the motherboard, and that worked quite well.

The rad is mounted to the top. HDD is in the basement, SSD on the back of the MB plate. Cable management is a bit iffy, but that's down to my inexperience. I did buy 100 velcro zip ties from amazon for about £4 - well worth it. The only real messy cable that is visible is the GPU power cable.

I'm not using the system for gaming, but so far when I've pushed the CPU (not overclocked, yet), the temps haven't been at all bad. That was my primary worry with this case, and so far so good. In worst case I can very easily take the front off to help with air intake.