Your spot sounds alot like mine only mine is about 1 square kilometer. I have groupings of only 5-10 per spot which are spaced out by about 300-600 feet (seems like alot but really isnt that far).

I have prepared each pot using both the hole method and the patch method. The patch method is easier but less stealth imo. For the holes i simply dig about a (1.5-2)x(1.5-2) foot hole, mix manure and some good potting soil along with the natural soil. I keep the composted manure near the bottom of each hole for when they need it later.

As far a diging I simply bought a nice good shovel and cut it down near the base making it perfect size for a backpack. Its alot of work but if you take the time to amend the soil well your plants will be happy.

Best time is probably the break of dawn as digging can be somewhat loud. Just take your time and avoid scraping rocks and you should be fine for noise. Allways have an excuse for being out there ready and dont leave any garbage. Be sure to keep in mind what your plot looks like from the air.

Good luck!