Ok, first lets start by taking those fittings back out and digging a little deeper hole. Why don't you tear that wood box form out also, gives you a little more room and no need adding termite food or somthing to rot. Looks like you have a sanitary tee laying on it's back for the lavatory drain, thats not to code in my area. Need to replace it with a combination wye-1/8 bend fitting. After that fitting you can not elbow up between the p-trap and its vent(creating an s-trap), you must continue with your 1/4" per foot grade directly to the p-trap. After the p-trap you can not elbow and run a distance horizontal like you have and elbow up again as you are creating a running trap or inline trap. Check the rough-in measurements of your tub, as most of them require the drain to come up just outside the wall not inside like you have it pictured.
Actually if the tub needs to be roughed in where you have it, you will probly need to break some more floor up. You may need to offset the pipe over to one side or the other for the lavatory drain so you still have room for the p-trap to swing back around to the tub rough-in.
On the 3" main drain.... 2 couplings and an elbow.... cut it in the middle of the horizontal run and again lower on the verticle and replace the elbow and the lengths of pipe needed to make it plumb. The use of a long sweep elbow might work also, or at least allow you to use only one coupling with it.
EDIT: after looking at your pic, "main drain #2" ... I can't believe you are not having any drainage problems with all the improperly installed sanitary tees on your main floor plumbing. The tees are recieving drainage and or improper venting from both their tops and bottoms and exiting out their side. Not good... hope they don't clog and need snaking, as the snake will probly just keep popping up at different fixtures instead of traveling down to the main drain. Oh, and stop going barefoot in a construction site
good luck with your project.