We are still missing a lot of info, like more precise goals, diet, training, etc.
But going off what we do know, and to keep it simple for you, I'd recommend adding between 375 to 450 MG per week, and running it for no less than 12 weeks.
Some things you're going to have to account for, in addition to what we know, are:
--estrogen control
--making sure that you're diet/nutrition match up with your AAS use (this is a whole other topic, and you'll be disappointed in your gains if you don't address it)
--training (same comments as nutrition above)
--run Test at least 2 weeks longer after you stop using deca
--YOU BETTER ADDRESS PCT BEFORE YOU EVEN START THE DECA!
Also, you better realize that IF THERE IS EVEN A SLIGHT CHANCE that you could get tested for AAS within the next 18 months, you need to avoid this compound! Deca use is detectable for a long, long time.
I know that the best course of advising you on the use of Deca would be to gather a lot more info about your situation first, but I don't get the feeling that you've really thought this through very thoroughly. Therefore, I offer the above input in hopes that you'll dig deeper into this.
Good luck!