Buy Craig Anderton's Electronic Projects for Musicians. This has a bunch of projects, and equally important, explains things like, this is a resistor, this is a capacitor and explanations like your guitar plugs in here, and the signal goes to opamp IC1 which amplifies 10x based on the ratio of R1 to R2, C2 cuts off the frequency above 50kHz, this then goes to IC2 which ....
One problem is that he frequently uses an opamp that can only be found at the end of the rainbow. It can be substituted just fine, but the PCB's will be wrong because the pinout isn't duplicated by any other device AFAIK. I think someone used to make an adapter and PAIA used to sell kits for all the projects, now only a select few that don't require the 4739 opamp. The projects are still valid, just only a few kits, and you have to etch your own pcb's or build them on perf board. GGG also has a PCB layout for his compressor using a different opamp. But that is an etch your own proposition. Etching isn't for me.
PAIA does have other kits, other pedals, and even a full blown synthesizer. I've built several of the CA-EPFM kits, and rack mounted them. I also built PAIA's parametric EQ and the "Hot SPrings Reverb" -- they also sell some of the kitsrus kits. I bought the two transistor preamp. I'm going to stick a transformer in front of it, and see how it does as a solid state, non-IC mic preamp.
Also, the white market at groupdiy. There is a guy in Denmark especially who produces PCB's for some of the projects, for example the "Bo Hansen DI" or the "DLA-2A. "
There are a bunch of projects over there, and PCB's for sale. They aren't exactly "paint by numbers" but there are a lot of really solid and helpful build threads, and a lot of amazingly knowledgeable and talented folks who post there.
As for mic modding, that's kinda my passion at the moment, and I've modded two MXL 2001's, a 2006, I'm going to mod a 9000 and I've just got all the parts for modding the HST-11a (the OEM version of the Apex 460) I've posted a few things in the DIY section here. As for modding other gear, check out the 6N3 buffer thread. Also at some point I want to get Tonepad's "Dos Ochenta" board, and well, mod it based on something I got on the internet....
***SHAMELESS PLUG*** I also had some PCB's made for a circuit that combines the G7 with the "Royer Mod" and have some left over. PM me if you're interested.