I think most, if not all, of these additions, were quite necessary. My league seems to be pretty active for a D5 league, so I think it was worth it for me to take on a higher payroll.
I know my players are old, but they should all be good throughout the season, and if I promote, my guards should be able to start for me in D4, and my PF could be a backup. Considering that I should be filling most of my seats throughout this season, I should make enough money to continue expanding my arena, bringing in even more money through the arena. Plus, once I promote to D4, I'll be getting an extra 200K. So, once I get to D4, there are pretty much two possible paths I can take. I can sell my old players, getting what I can for them, and just save up for a good draft pick, then relegate back to D5 with a lot of cash saved up that should be able to get me some nice, younger pieces for the future, and promote me back into D4 in a much better position. Or, I can continue to use my old players until their skills drop enough to make them unplayable. When that happens, I'll have made enough from staying competitive to pay for one or two young players with good skillsets. Not to mention the fact that I'll be training my C prospects for the next few seasons, and I'll probably sell one of them and pocket the extra money. Along the way, I'll be expanding my arena a lot to maximize my profits. So overall, I think getting a few veterans to promote out of D5 was the right choice, although maybe it would have been better to save up for a few younger guys.