At this point though IM undecided and feel that waiting to see how the d4 looks is wise
I think you will come to the conclusion to sell. After this season when his salary updates, it will be around 90-100k+. That is way too much for a D.IV center. My personal opinion is to try and sell him before than updates happens. That way potential buyers will be attracted to the high big man skills without being scared away by a huge salary (which is coming after the update). Then they will be the ones going "100k a week! That's way too much!"
So how often do you train on GS?
Never. Just make sure your players don't play tons of minutes every week.