I purchased a two unit house a little over a year ago and am looking to completely rewire the house. Currently I have a 100A box in the basement that has 3-4 large lines coming upstairs and then branching to multiple outlets and lights.

I want to put a 100A panel upstairs in a utility room that will be about 30ft directly above the panel in the basement. My father, who is not an electrician but very handy and wired his house as he remodeled, suggests feeding a 100A panel using a 100A breaker in the box that's in the basement. This would allow us to run new circuits off the upstairs box and abandon the corresponding circuits in the basement; eventually leaving the downstairs panel with only the feed coming in and then going out to the upstairs box.

From the upstairs box I could run new circuits up the the attic and then down to each room as I remodel (if going through attic is ok with code).

My questions:
Is this plan alright for code?
What size/type of wire should I use to feed the 100A sub panel?
Should this feed be run in the interior wall cavity or back outside and then back inside upstairs?
Is there a "more correct" way to keep the current circuits supplied and install a new panel upstairs that I can use for wiring new circuits?

Thanks in advance.
-Bob

How you want to run it is up to you. I'd be reticent to run things outside the house but it is technically legal as long as the wiring method used is approved for such.

Beyond that, if you are doing a major rewire, you should look forward a bit. 100 amp service for a multifamily dwelling is way below modern standards and you should look at upgrading that. Also, if the building really is 2 units, you should consider wiring them as such. eg each unit on separate panel that they can access. You might not plan on them being rentals now but plans can change or you might want to sell.

Thanks for all the info.