One stem, trunk, is good but several will work just as well. In your climate winter kill shouldn't be an issue so I'd probably go one trunk. Once the vine is on top the system you use is dependent on how much area needs coverage vs how much the canes grow each year. The simplest system is to prune like you would a normal vine. Head off your trunk in the middle of the arbor. Hopefully you then get at least 4 canes off the head. Position as needed for coverage. Those canes bear the next year. The following winter prune back as much as possible while still retaining 4 new canes for fruit the next year. The difference between normal and on top of arbor is how the canes are positioned. Normal they run down wires in two directions. On the arbor the canes are positioned so new growth covers area needed. They may pinwheel out from the head. You might have two heads depending on shape of arbor and area needing coverage. Once you get the feel for it pruning grapes is a lot easier than describing it.

For me the best time to plant somethings is in the fall. It give the plant months to take root before spring. Make sure to mulch the plant good to protect it from the cold.

Sounds like you might have a Muscadine (Vitis rotundifolia) it is a native wild grape of the southeast we have some here by our woods growing on some tree branches and I like them a lot they have unique taste. Pruning: Annual pruning must be severe to keep new fruiting wood coming and to prevent vines from becoming tangled masses of unproductive wood. The basic framework of a vine consists of the trunk, permanent arms, and the fruiting spurs. Vines must be pruned each dormant season to maintain this framework. Current season shoots bear the fruit, but to be productive, these shoots must arise from buds set on last season's growth, since shoots from older wood are generally sterile. It is important to leave the correct amount of fruiting wood. Pruning is basically the same for all trellis systems. Only the arrangement of the fruiting arm is different. Two systems of training are used, the upright or vertical and the overhead or horizontal system. In the upright system, a 3-wire trellis is used, the lower wire being 2 ft. from the ground and the others 2 ft. apart. On the trellis the arms may be horizontal along the wires or fan-shaped from a low trunk. With this system the cane is taken to the top wire and the first year or when vigorous enough, and then topped to make it branch. The resulting laterals are trained along the wire to make the arms. The overhead trellis provides more bearing surface per vine. The vines form a complete canopy about 7 ft. from the ground. The vines are trained to a single trunk 7 ft. tall with the arms radiating from the top of the trunk like spokes of a wheel. A mature vine will have about 8 arms. During the dormant season each year, cut back all shoot growth of the past summer to fruiting spurs 4 to 5 in. long. Remove shoots entirely that are not needed for spurs of fruiting arms. On young vines leave spurs of one year fruiting wood about 6 in. apart. As the vines get older, they develop clusters of spurs, or spur systems. Generally, thinning of these spurs is necessary after the fourth or fifth fruiting year. This thinning will force new spur growth to replace older spurs. Info: Muscadine Muscadine Muscadine Muscadine

My 3 yr old concords are getting very long canes coming off the main arms. Fruit has set on about the first 10 inches. With that said, what is the purpose of the remainder length of cane? Would pruning send more energy to fruit growth?