I too was thrown off by high gears closure, right around this time last year. Tried urban cyclery in e. Orange and I would recommend. I took my bike in a couple times, once for a tune up once for a repair — solid, reasonably priced service, friendly knowledgeable staff, and quick turnaround time.
I too was pleased with Urban. Free pickup and delivery as well, I believe.
Working on bikes is easy and satisfying. Have a look here: https://www.parktool.com/blog/repair-help and note that they make tools, so they may recommend more specialized tools than what you really need.
bought all our bikes at high gear bc of the free basic service. Hilltop quoted me something like $130 (if I recall) per bike. Just looking to get get family bikes running well for summer.
Any advice on how/where to bring or learn DIY? Lost. Without high gear.