As a former power lifter and strength coach for the University of Alberta Golden Bears Football team I hope i can offer some information.

12-15 reps would not be considered "high" reps if the last reps are max efforts,say at 75 or more % of a one rep personal best.
a set of 3 or 5 at this level is a very good and standard power building program.

The most important thing and the biggest setback to strength increase is INJURY! ALWAYS start with low weight and do 3-5 sets of gradually increasing lower weight to warm and loosen muscles and esp. joints tendons etc. Get the blood flowing. BEFORE you start to really work.
BENCH PRESS is the best exercise for gaining upper body strength and chest size PERIOD. DO IT!
It develops front deltois,upper pec,triceps,and lats
ALWAYS have a GOOD spotter and training partner! thats the second most important thing!
Endurance vs Power can be changed by varying the rest period between sets and thereby the weight you can do for the sets.
I used to do long sets on the bench up to one hour and 15 sets starting at just the bar and 20 reps and building by increments of say 2x25 pound plates. At 21 years old and 217 body weight i benched 440 on a world record of 497 (for under 200 lb bodyweight,held by franco columbo) with out steroids (LOL thats 25 years ago now!!)
Re push ups. Push ups are like bench press using about 75% of your total body weight,the % decreases slightly as you push "up" Bad part is strain on lower back and inability to quickly change weights for warm up and heavier lifting and inabilty to be protected and helped by a spotter or partner. The world record for consecutive push-ups (ie in a row) is about 14,000!!!!!!!
Regarding the pec deck. I have a complete Gym in my basement include commercial apex leg machines and weight stacks etc. I had a apex pec deck which is worth about $3000 brand new. I THREW IT AWAY!! (kept the weight stack off of it tho') they are SH1T an absolute piece of garbage for weight training. Best way to ruin your rotator cuff!! If you want massive lats and a wide chest BENCH,BENCH,BENCH. Of course genetics play a big role too, my 11 year old son weighs 237lbs and has a 52 inch chest and 30" thighs that are rock solid! (well for a kid) But big muscles ARE NOT what you want for boxing! All they do is tire you out!
Here's 6'4" and 297 pounds!