The first guy is fine. The price wasn't bad, and he'll be a good D5 starting center. He'll be good all this season, and next, before you would have to worry about skill drops.
As for the other guy, giving estimates of teh worth of a player on the transfer list is prohibited. But yes, USA players are good to have, as you will earn some of their salary back in merchandising (which you'll see in the economic update, on monday). As a prospect that player isn't that bad, but he has kinda a low JR, which trains slow, especially given his height (shorter players train most of their outside guard skills faster than tall players; vice versa for tall guys and inside skills). But he's a pretty good trainee.
Personally, I would suggest training guards, and looking for two 19 year old guys with allstar potential, and good levels in outside defense, jump range, and passing (inside defense is a plus too). These kind of players can be had on the cheap (5K and less to buy), and with one season of full training they'll be good D5 players, and with 2 seasons they can be really good D5 players, and decent D4 guys (add 3rd season of training and they'll be good D4 starters, and possible D3 backups).
Then I'd try and get one really good 18 year old trainee, who would be the focus of your training program. Perennial allstar or superstar potential is enough, and again with good starting skills. Often jump ramp, out. defense and passing take some time (and training slots) to train, so I like to find guys with good skills there. Then jumpshot, handling and driving can be trained fairly quickly.
Find another veteran big guy to play PF for you, and you should be in business. Now is a decent time to buy veterans, as at this point of the season the rush to get new guys is over (and people have spent their bonuses for promoting/the money they got from selling new draftees), but it's before the playoff eligibility deadline.