Not sure if it's different in the states (don't see why it would be, assuming still under the EASA regime) but 150h TT to start the CPL is correct.
I think the experience of hour building in a twin would be good, but honestly I don't think it's worth the amount extra you would be spending. The other problem (maybe easier in the states) is finding someone to let you rent a twin when you have virtually no experience. Think insurance requirements etc.
You can do a single engine IR as part of 'hour building' if you wish but bear in mind that you need exams completed for this, and you also need to make sure you're going to end up with enough PIC time for licence issue (hearing rumours that it will now be required to sit the CPL skills test). You do not have repeat the IR to get a multi engine version, but there is a conversion course as such. I believe it's 5 hours of which 3 can be done on a sim (from memory).
Lastly, theory before, during or after hour building is really up to you. I personally did the theory first doing maybe an hour a month just to keep my hand in, and then did the majority of the hour building afterwards. My reasoning for this was the I figured that the hour building was going to be the chance to be the most 'current' I ever had been to this point. Doing between 50-100h in a month or so should leave you very 'in tune' with the skills required, especially if you use the hour building properly to practice for CPL stuff (Cross countries to different places, different turning points, diversions in flight etc without a GPS). I think it is wise then to start the CPL straight after the hour building while you are still on top form, instead of doing the hour building, then sitting indoors doing theory for half a year then jumping into an airplane having done maybe a few hours in the last 6 months and hope to fly to CPL standard.