I'm bored on a call so I'll take a stab at a few of your questions. Greater experts should be along shortly to clarify.
55 watts is plenty to fill most indoor rooms at "comfortable" levels. If you like it loud, then you will want more power otherwise your risk clipping the amp and causing damage to it. Outdoors, you don't get any reinforcement from walls, so it can take more power to satisfy volumes at distance. It may be fine depending where you sit/stand in relation to the speakers but you will need to be more careful. Turn things down and consider investing in more power if the sound begins to sound a bit distorted or tiring.
I would hard wire, where ever you can practically do so. Cheaper than buying remote amps like Sonos in so many places. It's really budget and preference here though.
You ask if speaker wire is suitable for your distance but I can't see where you mentioned the distances. You can probably traverse your house with 12 gauge wire. If your pushing over 100 feet, then maybe 10 gauge, although you will find some wiring guides stating 10 gauge is good up to 200 feet.
You can't modify the Ohm rating on a speaker. At least none that I know of. The rating is the result of it's inherent design. It would not change unless you swapped out internal components.
You can change the omh level involved electrically enroute to the speaker by doing things like hooking up a second pair of speakers on the same run of speaker wire. It will basically double or half the ohms in play depending on if you wire the extra speakers up in series or parallel.
If your not familiar with this concept, I'd suggest that you don't try it until you research it a bit and can decide if this is both safe and desirable for your situation.
With great power comes Awesome irresponsibility.