Sarms are a good place to start for you. Umbrella labs has some great options. GW is great for fat loss and MK2866 is a great place to start for gains as well
Im no expert but basing off logoc with only one dose the blood concentration and is so low I hardly think it would cause an issue especially after a given time
We need a lot more context to your question. It's sounds like you havent done much research but id start by starting your own thread instead of posting on this old unrelated thread
GW cardarine is always a great addition for fat burning. SR9009 is also good for fat burning. Get your diet dialed in and add in some MK2866 or RAD140 for strength and lean mass and that will make a grrat first sarms cycle. Umbrella labs has everything you need
Running those while shutdown is a waste. You need to wait until after you are off the compounds and esters begin to clear for them to start working. Usually 2 weeks after last injection
There os defintely things you can do to decrease risk, but its certainly a risk of long term HPTA damage at your age. Thays why we recommend no earlier than around 25