Adding players before the playoff deadline is purely based on what your expectations are for the particular playoff matchups, and what your hope is for the next season. If you think you can add a guy or two and put yourself over the edge to win a championship, then you can. But you'll pay higher prices right before the playoff deadline as there's more competition to buy players.
If instead you are content to stay in your current league for another season (perhaps you want to work on out of position training for your trainees, or you want to build your arena and stuff- all while not having to worry about relegating), then I would buy some improved veterans after the transfer deadline. They'll be much cheaper then
So, in your case, I think with your team as is, you should be able to win and get to the finals. You beat Mamarenock in your most recent game, and that team has dreadful defense, so I wouldn't worry so much about him. The real question is whether you think you can be VCU Rams in the finals.
This is where it gets tougher. In your one game against him you picked exactly the right tactics, and on even effort lost by 12. Now your team has definitely improved since then, and you've been building enthusiasm. By team ratings his team doesn't seem to have improved as much, and it doesn't look like he's managing enthusiasm, so you might be able to pull out the wins. But your recent defense ratings haven't been that great, so if you do pick up some veterans, I'd suggest looking for some guys who have good defense (even 8 is good defense for D5, especially if the guy's secondary defense skill is decent - say 5 or above).
Hope that helps.