Way I always understood the old way is to plow to cut the sod and turn it over to put the weeds down where they will compost into the soil. Then disc to cut the sod, roots and such up into finer pieces for a smoother seed bed. Then spring tooth or spike tooth harrow to form a consistent and reasonably even surface for final planting. Also in there could be a subsoiler or chisle plow for breaking up and aerating the hardpan, mostly for deep root crops. There is a seperate implement for making rows called a row hipper or bedder. All this hapens before planting. A cultivator is used to control weeds after the planting, and come in many forms including disc, tooth and plow types. They can also be used for aerating the soil before planting. Cultivators generally are set up to disturb the soil between rows and have specific row spacing although there are exceptions. This is the way we reclaim old hay fields, rototillers do a nice job as well but are harder on the soil, and we have all the old equipment but no rototiller. We also do a small garden plot but spend more time changing implements than working the garden. As to HP that depends on a lot of factors. I have an old ford 3 point 6' tandem disc that will stand an 8n on its rear axle quicker than you would believe. I saw some 8' discs at tractor supply that I think you could double up behind an 8n. I think on your tractor you will run out of traction a long time before you run out of HP. That is common with compacts, ballast will help.
Sorry about being long winded!!!
