Re: Japanese maple's leaves are turning green
It's difficult to generalize, but to give you some pointers: if you say the leaves are turning green, I assume they were red when the tree first arrived. This is normal, since most red japanese maples start out red, turn green, and end up with a different red in the fall. One of the attractions of these maples is the change of color.
It's best to put trees in the ground when the tree is dormant (fall or, possibly, early spring but soil temps play a role) but here you are. As regards moisture : keep the soil moist (cool) but not wet (for me that means every 4 or 5 days), for you possibly more often - check every day and you'll get an idea. It's good to take the time and keep monitoring. You don't want it to dry out, but you also do not want to 'drown' the tree: the adverse results are pretty similar in both cases, since roots need moisture AND air.
Mulch the tree (not sure whether you are a maples novice, or a gardening novice, so forgive me if I state the obvious).
About fertilisation: I wouldn't use any plugs. Have your soil sampled - have it analysed by a lab (I'm not sure how to go about getting this in the US, but people here on the forum, or a more ambitious gardening center, can tell you. Where I am I have the option of going through such a center or bringing it to the government lab... I remember people mentioning the 'local extension office' in the US ). Then only think about fertilising - you might not need anything much at all.
About the sun: avoid afternoon sun. If your maple gets too much sun, you might have to move it, or plant another more resilient tree in its vicinity to provide afternoon shade.
Keep the roots cool, and take the time to read through this forum: you'll find most answers to your questions.