Hi! I think you're doing pretty good, especially for just starting out. Let me tackle your questions:
1) This shouldn't hurt at all. You said yourself, you're doing it to stay sane. There is (in theory) a bit of a downside to it--by eating a candy every day you are making sure your sweet tooth continues...But you know what? I have never been one of those people for whom anything but chocolate would cure the craving for chocolate. You're doing a great job of sticking to one
small serving, and you are staying within your calorie range, so there's not really anything to worry about, IMO.
2) Ah, this is one you are going to get conflicting answers on. There are some claims that diet sodas have a similar effect on your body as do regular sodas...that the sweet taste primes your body to want
more sweet things, or something of the sort. I don't subscribe to that theory. I need my Diet Coke. No one gets hurt when I get it.
Honestly, back when I lost 70 pounds (I've gained back 30 of it...), I did it while sucking down diet sodas, so personally I haven't seen any indication that diet sodas will stall weight loss, and I know
so many people who started losing weight rapidly once they stopped drinking their calories.
3) You are doing fine with your exercise. Don't forget to count those stairs as exercise--they are. Do what you can, and don't get down on yourself for not doing what you "should." You already plan to work your way up, so there's nothing to worry about. You should be able to lose weight with any little bit of exercise added in.
4) Of course not! Now, to keep motivated you will probably need
some sort of measuring device. Have a tape measure? If not, buy one--they're ridiculously cheap somewhere like Wal-Mart or Dollar General. Track your waist measurement, maybe also your hip measurement. Failing that, take a piece of string and a ballpoint pen and make marks on it.
Or use a certain piece of clothing. Or--and honestly, this is probably the best--concentrate on how you feel with your improved eating, and don't worry so much about measurements.
Now, on the gym front. If there's a YMCA near you, talk to them. They have a 'scholarship' program for memberships that is based on how much money you make. We're paying something like $14/month for a family membership. If there's only one of you, it may well be even cheaper, and hopefully something you can afford. This will give you access to a gym, a lot of classes, and a scale. It's not something I'm saying you
need to do, mind, but it's an option.