Do the Red Sox need to make some roster adjustments? Absolutely, regardless of how the rest of their postseason run goes. But to trade away their best, young, cost-controlled players for veterans for one or two years of playoff runs is one of the dumbest ideas in the world. In order to get on the same level as the Yankees, Astros, or Indians, the plan would be to do what they've done: trade away bad contracts for lottery tickets and draft well. The best way they can improve quickly is to start dumping under-performing veterans on expiring deals and maybe trading one valuable piece that might be a bit redundant for the hope of getting some young players back who might blossom into eventual ML replacements. Losing Hanley this off-season and finding a new DH or just using the position like everyone else in baseball does will be a good start. Porcello isn't going to have as bad a season next year as he did this year and I believe the word will come out once the season is over that he's had some nagging injury that will partially explain his struggles. Doug Fister is a likely candidate for a 5th spot/swingman role on the cheap but I think he's likely earned himself a two-year deal somewhere else.
Dustin Pedroia also looms as someone who it might be time to move on from or to drastically lighten the workload of, having him platoon 2B or DH (which might be best for him in the long run) with someone like Marrero. Some of the bullpen will be turned over because it always is. Steven Wright might come back healthy, Blake Swihart will have had a full year to get better and might see some AFL time if he's eligible, and some of their better prospects will be a step closer to being ready. The team may take a step back next season and barely contend for a Wild Card spot, maybe for more than one year, but will, ideally, then become perennial contenders for awhile. If they do everything you suggested, it will be years before they are more than a .500 team.