You will be purchasing a kit, which is 10 vials. The number is the amount, in mg, that is in each vial in the kit. So from the AmoPure site, the L30 would be tirzepatide 30mg x 10 vials. Be aware of what dosage you need, as the 30mg may be too much for someone starting at 2.5mg. Everyone has a different personal tolerance level for how long they use a vial, but the best practice would be 28 days/4 weeks. The calculator I link below will tell you how many doses you can get out of your vial when you specify the dosage amount you need.
There are several calculators around for figuring out the ml of bac water to add. You will need know what your dosage is going to be per each injection and the amount in mg in each vial, then you can adjust the amount of bac water you need to add to determine the number of units to inject. Most amounts I've read about for these smaller peptide vials would be 1ml to max of 3ml, maybe even 2.5ml max.
Calculator is just one of several I have used.
There are many reputable sources for bacteriostatic water, Peptidetest.com is one I've used personally, but search around these forums for any suggestions and also many medical supply websites will sell it. Ensure you only use Hospira brand, and check the expiration date. It is NOT recommended to purchase this from Amazon as they sell "reconstitution water" or "sterile water' and that is NOT the same thing.