sustanon needs to be injected EOD or ED (every day) if you want to have the most stable levels. it can be done once or twice a week also BUT your levels will be more uneven. will it matter much? it could and depends if you want to do things or do them really good.
1 bottle of sustanon is 10ml so yes 1 bottle if you inject 2ml per week will last you 5 weeks, thats basic maths