I have been here ten years, most of that on tourist visas. You assume some risk but I find it worth it. You may not be able to do unlimited border bounces (or you can, nobody knows), but if you're creative and determined you can stay here a long time on tourist visas.
Turn off the airconn. If the house is warmer the water will seem less cold. I have two showers and the water heater broke in one, I continued to use it for a couple of years before I bothered to fix.. Not hot showers is not the same as cold showers, you'll be fine.
They will likely cut off a hand if you miss a check-in, especially if you're in another country.
Check-ins are for 90 days in the country. If you leave, you are not in the country. The last I knew (things may have changed), you do check-in when you return..
I would not change your flights. You should be good to enter on visa exempt.
If/when your DTV is granted, you will need to exit/re-enter Thailand to activate the DTV.
If you have no travel plans you can go through an agent to a near land border, cross, come right back (border bounce). You can do it yourself also, if you're into adventures.
I think you will be fine. If they pull you aside to ask more questions, play it cool. Explain how much you love Thailand (as you did in this post), explain your employment/life doesn't allow you to live their full time, but you enjoy spending your free time in Thailand. The immigration officers like hearing good things about their country.
I think people run into problems for one of two reasons, A) They're assholes who think they are entitled so they become combative, or B) they have a problematic history (black listed, then arrested, then ....).
You seem like a decent bloke who spends money in Thailand, you're exactly the kind of people they want in their country.