don't get in over your head. every plant requires attention 70% of that attention is hauling dirt to the spot. unless you find an area with good black dirt.... this is VERY important, and the difference between harvesting 1/2 oz, or 1/2 lb per plant. i would say twenty is alot to handle for a first timer tho. just do as many as you believe you can give a 2x2x2 hole (you can go 3x3 if your really ambitious... it will pay off) of good dirt to grow in. light can also make or break your harvest. don't plant in the middle of the woods where the plant wont see more than 2 hours of sunlight a day. try to find a spot with at least... AT LEAST 8 hours of light a day. a good way to see where the sun will be where you will be growing is to point your arm directly east where the sun will rise, and follow the path the sun will take. at mid- day the sun will be slightly to the south....not straight overhead so take that into account. the southern side of woods can work very well, as it provides the cover of the woods, but still allows southern exposure for maximum sunlight, and maximum growth.
if you have problems with deer use high strength fishing line(80-100 lbs) as a discreet fence.
and if your in the southern part of the state transplant outdoors around may 10th, give or take a week depending on weather. (if your not in the south find a "last frost" map of mn, it gives you the average last frost date for different regions of mn)
....i hope you picked strains that finish before the first week of october. it would suck to see a 10 foot tall monster go to waste because it got a heavy frost 4 weeks into flower
well thats about all i can think of for now. good luck bro, and i hope you do well.
lets show what mn can do