To your second question, boiling previous then adding later, I can't see an advantage to doing this so I would skip the step, the disadvantages would mount quickly.
I will say this before getting into your questions. If your beers taste bad to you, I would look to other processes to improve your beer before adding complexity to the process. Sanitation, sanitation again, then sanitation again, then yeast health/pitch rate/temperature control, then look at your sanitation again, then maybe look at the water you are using. Adding complexity will increase the number of variables you have to adjust and re-adjust each time you brew and you'll have a harder and harder time getting your process right. I've had beers not turn out how I wanted them to turn out, but it was mostly process and recipe that got me, sanitation was one of the steps I've almost never had issues with (random gushers yes, and two beers that got infected with brett but that wasn't a problem cause I could turn around and use them for another experiment). Don't be so down yourself, took me about 15-17 batches before I made one that I was like "Wow, thats damn good, and it turned out exactly the way I intended with my recipe".
If the end goal is added hop character (aroma/flavor) I would just utilize a sort of poor mans hop whirlpool or hopstand. If you had some frozen wet hops (fresh not dried hop cones/pellets) they may help cool the wort a tiny bit if you are adding them during cooling, but the main advantage is you'll amp up the hop flavor and aroma. To simplify the concept the hopstand/whirlpool you take your wort after the boil is over and start cooling it, some people throw their whirlpool hops in as soon as they start their cooling, some (me included) cool the wort down to 170-180F then throw in the whirl pool hops, give the wort a really good stir then leave it for 10-20 minutes. You'll really really amp up your hop presence in a beer without adding a lot of bitterness.
