if it's your first cycle 300mg per week should be enough to make some reasonable gains. imo 400mg per week and a shorter cycle will probably benefit you more.

if you eat right, 300 - 400mg of deca each week will probably help you put on a few pounds each week. but the deca won't really start to work until week 3 to 4.

are you sure you don't want to throw some dbol or test in there? would recommend dbol to kick start your gains in the first 4 - 5 weeks.