I would keep the guy you just bought because when you sell a player you only get a percentage of his selling price, and if you sell right after you buy you are only going to get around 80% of the sale so you will probably end up losing money. You can build around him though. Older players (30 and over) are cheaper to buy than younger ones so this purchase isn't really too bad. What I would do is trim your roster to around 10 of your best players. Then you probably need one more "decent" player (weekly salary of around $5000 - 8000 per week) and you will have no problem doing well in division V.
You also could find a cheap trainee (a player that is young, proabably no older than 20, 18 is best, with at least star potential) that you can train along side Dan Roe.
To answer your training question NEVER do team training unless its free throws or stamina. Team training trains everyone on your roster, but hardly anything compared to one postion or two position training. So always do one position, in your case guards, or point guard. Also in order for a player to receive the maximum training he has to play at least 48 minutes each week.
I mentioned this before but you really need to read the Guide to Buzzer Beaters if you really want to understand the game.
Hope this helps