Hi Walter;
Welcome to Permies! and to the wonderful world of Rocket Mass
Heaters!
I'll try to help answer at least some of your questions.
#1) Where to get wood?
Oh my gosh wood is available in many places once you start looking. Free
pallets , construction waste , tree trimming company's, sawmills, and of
course just buying split & delivered cordwood.
#2) Home modification's needed?
Your home needs an 8"
class A roof jack & insulated chimney pipe to go thru your roof.
This is probably the most technical & costly part of a RMH build.
Depending on your floor you might need extra support for the weight.
#3) Codes, resale, contractors?
A good looking, properly working RMH would assist with resale.
Building codes vary wildly from state to state, calling your stove a masonry heater will help ease the way to compliance.
Contractors able to properly build a RMH are few and very far between.
Tell us more about your location, wintertime temps, the design of your home.