Depending on the space you have, and how much the plants will stretch after the flip, you can leave them in veg to whatever size suits you. And you can at this point go either way with the light type, given that the HPS probably has more lumens, it wouldn't hurt at all to veg them under that for a week or two.
To make them more bushy requires training. I involve multiple methods for bushing up my plants. I stat by letting them get about 5 nodes tall then either top them or FIM them. Topping will produce double colas on seedling plants, but on cloned plants I perfer to just FIM as that causes all of the lower branches to shoot out and up rapidly. Once the branches get 8"-10" long, I use garden ties to pull the branches down and open the plant up. This causes multiple branching to occur.
Then once the main branches get shooting up after being tied, I go to the top few inches of each top branch and gently crush the stem between the leaf nodes, just enough to be able to bend the top growth of the branch over sideways(this is Supercropping) which slows the upward growth and encourages the smaller branches to take off growing. Within 48hrs the bent branches will heal themselves and stand right back up, and the stems will be even stronger as they build around the damage in the stem.
If my plant still is not as bushy as I want, I will either Supercrop it again or FIM all of the topmost branches. This process can be done extensively to greatly enlarge a plant's girth, or it can be done just a little to make it a little more bushy. Each technique applied will add about a week to your vegging time to allow for the plant to recover before putting it in flower.
Hope this helps
