I'm happy to help. You want this:
Peptide Calculator (Beta) ⋆ Peptide Reconstitution Calculator (Beta)
So if you have 5ml semaglutide, you can add 2ml of bacteriostatic water and then draw 0.1ml (or 10 units on an insulin syringe) and that will be .25mg.
If you add 1ml if bacteriostatic water, then .1ml would be 0.5mg.
Yes, semaglutide has a very long half life so you want to inject weekly. That said, some people who complain of nausea after the injection say the symptoms are less severe if they divide the dose in 2, with injections 3.5 days apart.