You do not get Lovis' tower, but another one. It is available after you finish Maxos temple. Bringing Lovis his soul stone is not required for that (there is also an alternate solution, as you'll find inside Maxos temple, though not necessarily a better one).
destroy the stone and you earn the gratitude of those that asked; return it and Lovis unlocks a chest with a random legendary quality piece of equipment
After Maxos temple you will be able to freely travel around for awhile, but at a certain point (which you will be warned about in-game), you will no longer be able to complete most quests in Broken Valley, and will need to clean up anything you have left to do first.
There is a necromancer in Broken Valley, but you'll have easy access to a different one in the tower.
You can create a creature with just the basic body parts provided by the necromancer, but it will not be very strong. Once you have the battle tower there is a merchant there that can sell body parts (save before running the crosshairs over him, and you can reload to get an upgrade or two each time you level). Actually, the stuff you sold was probably lowish quality; if you keep an eye out for better quality stuff, you should find a few decent parts before getting the battle tower. When you talk to the necromancer any non-duplicate parts from your inventory get added to his list, and are available to use. I kept a written list handy with my best parts for each category, and sold lesser parts before talking to the necromancer to work on the creature (no sense cluttering up the parts list with stuff I'm not going to use).
