Yep, as buzz said, 3x/wk, full body resistance training is good for str&con.
Now, more specific Q's once again. I apologise for how long-winded this will be, but I need to demonstrate the importance of truly understanding your goals. What sort of endurance are you looking at? Why are you looking at endurance? Do you want to run a marathon? Do you want to survive 5min in an MMA fight? Do you want to be able to maintain max speed while running? Do you want short-duration muscle endurance (1-2 minutes)? Or were you just told that endurance training gives you a better appearance (if so, I'd think twice). Endurance training should be all about performance rather than appearance (which there are better ways to achieve), and as such should be specific to your endurance goals.
As for gaining muscle in a 3 month span. Most people can gain muscle in a 3month span, the issue is how much you expect to gain. The amount may vary, but given that you've been out of training for a couple years, the right program an nutrition could see you gaining 20 lb in that time. Inclusion of endurance training may hinder your ability to gain mass though, so if you focus on both goals at once, maybe only a 10 lb gain (depending on the program design). It's probably best to focus on one, then the other, especially if you're looking at marathon-level endurance.
However if short-duration muscle endurance is your goal, then perhaps 2 sets of 5 reps (for strength) followed by 1 set of 25 (provided technique allows for it; maybe start at 10 reps and build up to 25) could work both goals simultaneously without hindering gains in strength and size.