As a plumber/gas fitter i'd suggest you still add the gas RI's to the gas stove and or gas fireplace,maybe a garage heater, as maybe someday down the road you will get gas then you are covered. Are you running propane for heat? you can change the orifices in gas stoves to go propane if this is the case.
Also as a plumber ,yah i suggest you get all plumbing and water RI's done at the time of initial RI. Basement bath,RV sewer ,HB's waterlines to fridges .watersoftner etc is a lot easier to do at the start as opposed to doing later. Yes a little more money now but worth it in the future.
As for a water heater,our standards have to be all High efficient waterheaters which in watertanks are nothing but trouble as most are poorly designed,You maybe should look into a Demand type water heater or better yet GET a Boiler and also slab heat basement and garage for Comfort or go all out and Slab heat the entire house. Definetely the way to go but cost can be up there.