Sound generation (VCOs, noise, etc) and sound processing (filters, phasers,overdrives...) are generally good candidates for analog implementations. People will argue that DSP is more accurate, which is true, but the little nuances of analog circuits (pitch instability, possibly noise or intermodulations and so on) do make a difference and produce a character. Filters and distortions in particular sound absolutely shitty, empty and uninteresting on digital synths.
VCOs are a very hard thing to nail. Exponential VCOs (1V/oct standard) are VERY depended on temperatures, which will be your greatest problem. Tempco resistors are a solution, but thermal oven compensation is more straightforward and works great (and maybe, better?).
I suggest investigating the sawtooth core topology, because of it's low price and easy to find components. Triangle cores can be a bitch to perfect and are certainly more expensive.
Filters come in all forms, prices, shapes, just google some and use a verified design. The moog cascade filter is an absolute classic in synths and it's not much of a hassle at all.
VCAs can be designed in a number of ways, one of the most economical is to look at the LM13700 (or CA3080) applications.
Distortions can be as simple as a diode clipper/fuzzer, but you can get more fancy if you care that much.
Control signals (sequencers, LFOs, envelopes) can all be made with analog/discrete components, but since you have digital skills, just make them with a processor. You will have advanced functions like syncing to external tempo/clock, phase difference between LFOs, sequence save/recall etc. It is also considerably cheaper to do it that way.
Various flavors of noise are used, a simple "white" one can be made using a couple of transistors and resistors.
YUsynth has a ton of stuff and projects available on his website, along with schematics, boards and short explainations. There you can also find the full schematics of the microbrute and mini brute synthesizers. Both are commercial, low cost synths that combine analog and digital methods (analog sound-digital control. kind of.) and can teach you more about synthesizer systems architecture.
Knowing the LM13700 is an absolute must in this field, as well as differential pair applications in general. Have a SPICE simulator by your side at all times- it will help you a lot.