Parallel Capacitors-Theoretical Question

That 13uf electrolytic cap is 20% tolerance, a 12uf would probably be fine.

I gather that the results of adding bypass caps are unpredictable. Some reviewers (Auw Jimmy, Jon L. & Tony Gee) make the analogy of usng spices in cooking. They experiment until they hit upon a sound flavor they like.

I was really trying to get away from experimentation, it gets too costly. I realized that after rolling op-amps into my phono preamp recently. Before I knew it, I had spent nearly $300.
Capacitors are a bit more complex I think. There are more issues than their face value that can affect them. For example, Mundorf interleaves their capacitor's windings to cancel inductance. After I read that, I wasn't sure what might happen with 2 caps in parallel. Would they induce each other and do strange things at a particular frequency? There's also ESR to consider.
Although I realize many designers make their component choices from an economic standpoint, I still respect those choices as being the best available at the time to get the job done. After all, isn't engineering the art of compromise? That's why I wanted to keep the 13uf value, or get as close to it without causing other problems. It would therefore seem that a good 12 uf capacitor would be the place to start, maybe add 1uf to see how it changes things, and maybe add a bypass 0.1mf after that.
Thanks for your help guys. If anybody's interested in the final result, contact my email and leave me a message.

Capacitors in parallel are the same as resistors in series.

Al shouldn't the tolerances for cap add in quadrature? (0.1^2 + 0.1^2)^0.5 = 0.14 or 14%?

kind of ticky tack, sorry. I'm more curious and electronics are not my field.