Looks like you have it pretty well figured out. The shower and lav drains should be 2" and the weir of the shower's trap cannot be further from the lav drain than what is specified in your code. I would put a cleanout tee under the sink also.
The below-grade connections from vertical to horizontal must be done with wyes, not tees. The water closet bend will not likely be directly over the main drain, nor would I want it to be. You will have to work out the distance and angle to make the connection.
If I remember right, MA is one of those states where a homeowner is not allowed to do their own plumbing. This is a legal issue you should consider as doing a full bath without permits and inspection could wind up being a very expensive mistake.