Congrats on the baby. Our first is now approaching 3 months.
I have a 1.5HP DC hooked up to the 6" metal ducting you can get at HD & Lowes. I believe its either 22 or 26 gauge - it really doesn't matter. Some joints I used a little bit of caulking in and then used duct tape over the joint, others are just duct-taped. There are arguments over whether duct tape is okay, versus the dedicated foil tape. I used what was less expensive and worked for me. I find that the adjustable elbows tend to leak a bit more than other fittings, but I just tape them up to minimize leakage. I did caulk the joints on wyes to make them airtight. With 2HP you should have plenty of suction. The metal ducting is relatively inexpensive, especially when you compare it to pvc.
The only expensive piece in my system is a 6x6x6 wye that I had to order. I avoided using tees as they are not efficient.
I basically use a transition fitting to go from 6" down to 4", and then either attach a blast gate or a plastic wye, the plastic hoses.
It not the greatest looking system, but it works well. As far as static issues, I have gotten small zaps in the winter when it is really dry. Where there is enough humidity in the air, there is very little to no static to worry about. The theory about grounding has been debated for a long time! DC system design and construction can truly overcome fears and concerns, but it really doesn't have to be that elaborate. Just make sure you properly design the size of the ducts. Bill Pentz is a great resource when it comes to this. Just keep in the back of your mind that people tend to go to the extreme with fears (some are very legit) to the point where they would rather work in a clean room where one would make computer chips!
Good luck.
