Not a stupid question at all. I started with 60mg until I was comfortable enough to handle stronger Nic. I'm careful, and now I buy 100mg Nic because it's cheaper and lasts much longer. You should only buy what you're comfortable working with, but you shouldn't get something close to what you vape unless you don't plan on mixing much with it. If you vape 10mg and buy 12mg you're not giving yourself much room to add much before your Nic will be less than 10mg through dilution. Get a decent calculator, and dilute whatever strength you buy down to a decent strength with PG or VG into a base to mix flavors with. It's pretty easy, and you'll be amazed at how much mulah you can save.
Sent from the hand not holding my vape