Crap, I could have read your original post and gotten half that information. Sorry about that.
Well, there are a couple of different routes you can take. You can go the total body, HFT route or the split route. For adding mass, I'd say the high frequency training route is a better road. The idea is to hit each set of muscles multiple times a week. I'd say five is ideal. Use a combination of single joint and compound movements.
Don't use the same movements for the same body parts on consecutive days. For instance, if you do squats one day, do lunges the next. If you do barbell bench press, then do incline dumbbell the next. So you attack the same muscle groups everyday with different exercises.
If you want to do splits I would do two or three day splits. Upper body, then lower body. Or, all push one day then all pull the next. The advantage hear is you can get more focus on fatiguing each muscle group more completely.
As far as exercise selection, I'd stick with the basics, squats, deads, pull-ups, the many variations of bench, overhead presses, the many variations of rows, pull downs, curls, dips, etc.
As far as set/rep schemes, I'd recommend either 5 x 5, or 10 x 3. The Idea is to do 25 to 30 reps per exercise, but error on the side of doing them heavier.
Lastly, go the "Authors" section and look up articles by Thibaudeau, Waterbury and Poliquin. There are many good authors here, but in my humble opinion these guys are on the cutting edge. Browse through them and pick ones that peak your interest. You cannot go wrong.
I hope I was some help. There are many good ways of training; you have to find the right one for you, which is not what you have been doing for years and years.