Quick update, got impatient and decided to just take some 70% ipa and clean the leak by the adb ports as it seems that is a common issue for soft power and it booted right up!
Will start removing the old caps this weekend, but always good to know its in a working state before you start.
Still no dice
I have noticed one bigger issue. In the Dead Mac Scrolls (Troubleshooting, flup-flup- issues, page 24) there is a description that one should be able to measure a lowish 31/30 ohm resistance over the CR20 rectifier diode. And 52/53 ohm across CR21. If I try to measure that on my board, I briefly get about the correct value but then it starts rising, and ends up somewhere over 2-2,5 kOhm. I can't quite figure out why, as I have replaced both CR20 and CR21, and the electrolytics around them.
Also adjusting R56 (+5V adj) fully counterclockwise (page 27) does not help the issue.
The Booti is the best current way to go for HD emulation. It's currently out of stock but you can get on the email notification list for when it's back in stock which should be fairly soon. You could also go with the ReActiveMicro MicroDrive/Turbo, but it's harder to get programs onto the CF card, whereas with the Booti you can just swap a USB thumb drive between the GS and your modern computer to get stuff on there.