When building your own modules, you're not designing anything. You generally can buy the faceplates, circuit boards, and either supply your own parts or can buy a kit that's ready to assemble. The only challenge would be kits that use tiny surface mount components. There's a micro - Eurorack group on Facebook somewhere that has all kinds of builders recommending and helping each other.
Mixers are a good thing. IMHO you need two mixers. One for summing audio and or CV and a larger stereo mixer as your main mixer. There are a TON of options. The caveats are how much space and much money do you want to spend? Pittsburgh's Lifeform's, Blue Lantern's Stereo-Sir-Mix, Happy Nerding's mixer (forget name), Roland's 6 channel mixer, etc. Some include line-level outputs built in, some do not. Some have more aux sends than others, some offer modulation of pan or volume level... others don't. Some have headphone outs... others don't
I bought the Blue Lantern option because I wanted more sends and the price was right. I'm happy with it. But it lacks headphone outputs, CV modulation, or line level outputs. But I didn't want them in my mixer (personal preference).
The MIDI to CV option is always great. You can go as low-end or high-end as your needs require. 2HP makes a small, simple MIDI to CV converter with a USB-C input. I use an Expert Sleepers FH2. Either option is good. It just depends on how deep you want that tie to be between your DAW and your rack.
Please note the most current Disting is the Mk4. Be sure you're buying the "Mark Four." Development of the prior versions has stopped and the Mk4 still receives regular firmware updates. It's not worth it to save a few bucks on a Mk3 IMHO.