Not a silly question at all, Zissou!
There are a few "beginner's" guides on parts stocking & sourcing, such as at Beavis Audio, Aion FX and GuitarPCB — check them out.
Start familiarising yourself with DATASHEETS of what you're ordering. For example, you see a deal on some 470n caps so you buy a bunch but when they arrive they're too HUGE. Well if you'd checked the datasheets you would've seen those caps on sale were for 1,000v, and all you really needed was 50v 470n caps... you can imagine how I know this.
Just know that you WILL make a few mistakes when ordering, to begin with, but you learn from those mistakes and if you keep the "mistake" components you may eventually find a use for them, even if it's paying a freebie forward or barter exchanges for something you need etc.
Don't worry about not understanding everything on the datasheets, either, that knowledge comes with time & experience and some of the data isn't too relevant in the bigger picture of pedal building.
Parts-Kits are a good way to start, but you'll soon find they've limitations when you run out of one particular thing and find you never use another thing the parts-kit supplied. As BuddyTheReow suggested, the kits are a good idea to see what's common, yet still order items independently.
I tend to go through a lot of 1k, 10k, 100k resistors, as well as 4k7, 47k and 470k...
A100k is a common Volume pot
B100k is a common gain/tone/etc.
If you play bass, get some extra box-film 220n caps to sub out for 100n, 1uF (and 2u2 if you can find them)...
Yeah, user guides.
PT2399 delay builds, the ICs aren't that reliable, sometimes you have to swap a few in/out to find one that works well with a build, even though all the PT2399 chips you have may work, technically.
4049UBE is a pretty popular CMOS chip with a number of different OD/Dist/Fuzz circuits.
Ahhh, check out those aforementioned Docs, they mention everything I've just suggested.
Nota Bene: No matter how well-stocked your pedal-parts larder, you will always find builds where you need to order one part, and that one part will NOT be from your main parts-supplier — there is no spoon one-stop shop.
Happy parts hunting.