Is it ok to play some of my best players both ways, or do players fatigue easily in this game?

Thank you, I wasn't thinking about that.

Does the same logic apply to special teams? (ie: are there bpos setting for punters, kickers, and gunners?)

From a long term point of view, it depends on what your plans are for the player. Players can only gain BPOS points in 1 position per game. If I'm not mistaken, the position gained is defense first, then offense, then special teams. So, if you have a player playing defense and any other side, then only his defensive position gains points. If he doesn't play defense, then his offensive position gains the points.
So, in order for a player to fully develop at his position, it's best to play him only that position at least until he's fully developed. So if this is a player you plan to keep for a long period of time, then it's best to pick one position and leave him there for a while. If the player is a stop gap until you find better players, then I don't see a problem playing the player at multiple positions.
Personally, the only useful reason I can think of to do this though, is to keep your roster very small to save money.

of course there are exceptions take a look at who is kicking for the UK in their games

weakestlink33 wrote: Thank you guys

anytime good luck