Well, you have a project for sure. First, kinda decide how you are going to utilize this tree. Doesn't look like you will be able to keep the height down so here's my best advise. Do your pruning, major make over, in the winter when the sap is down.
Cut those suckers off as close to the ground as you can. You can get some special paint to stop the tree from growing more suckers in the spring but you will have to keep after it. Also, as you remove the old suckers check to see if they have rubbed the bark off of the main tree anywhere. If so, you should put some topical covering over the bare spot as they will weep in the spring attracting insects.
Cut the lower limbs off as high as you need to to be able to walk around the trunk area easily. If you want to limit the tree's height you may have to rent a lift of some sort to get you safely to the higher branches.
Most likely this tree is bound up in branches. As you work your way up through the tree pick 4 or 5 main branches to work with. Eliminate the rest. As you work, same thing applies as with the suckers. Look for limbs and branches that have been rubbing and cut them out. Insects love the sweet nectar that seeps from this kind of tree.
When you are working this tree over try to visualize a "canopy" of smaller branches, leaves and fruit growing from the 4 or 5 main branches you saved. Hope this all helps,best wishes.