It is based on the position. You'll be a step 12 unless you're an IP, in which case you'll start at a GS-13 assuming the job is listed as "Airplane Flight Instructor". You could possibly start at a Step 3 if you have extra qual's (example: RTU unit and RTU IP experience), but it depends on the local unit policy.
See above.
Go to opm.gov, search pay tables and special salary rate, 2181 series, and it will break it down. searching 2181 also works
yes, but only for days on a mil status: UTA (drill weekend, $21ish dollars per period, 2 per day), AT orders (21 per day, or what you are getting per month now if you get on orders >30days, AFTPs (same as UTA, limited to 36 per year, 12 per quarter).
yes for >30 day orders
Yes, opm.gov has the answers, click on health care tab for gov employees, will let you compare plans and list monthly or per paycheck expense.
The job you are considering should be advertise somewhere, ask the unit if you haven't been told where to find it. It will list a pay range. Ball park figures for ART pilots: $89-112K probably, the mil pay listed above is in addition to this figure.
It takes about a year to figure out the system, find an ART that's been in the system for a while and have them show you how to fill out a time sheet, an AFTP form, and log comp time. You also get 120 hours of mil leave per year where you can "double dip" and get paid ART pay while you are also on orders or logging and AFTP/UTA.
There is too much to type, the answers are in the Technician Handbook, which is probably available online. I've been an ART since '08 and still learning the system. It's not as easy as getting the DFAS direct deposit you've been used to on AD. It pays to always double check finance, they make mistakes frequently and often, especially in the world of two pay systems.