@schizo
I went through this last summer so I'll try and answer what I can.
1/2. I believe they charge $1000 application fee for each additional membership, I would imagine buying a seat you currently lease would fall under that. I believe this is also the fee if you are a lapsed member, but fwiw, at least with my seat (cbot-GIM), the lease was negotiated for like 10 years and requires a 2 month notice to cancel. Other seats may be different though.
3. Yes the exchange would now consider you a professional. (though contrary to what someone else posted, this has absolutely no barring on your taxes, its just an exchange designation)
4. You are highlighting the fee to trade in the pit. If you buy a membership and trade through globex you pay 0.35, if you lease I believe its slightly higher at 0.47. This doesnt count your platform (cqg) or clearing fees. If you are doing enough volume to justify a seat I would estimate you would be paying around 0.7 for clearing, platform, and exchange.
5. This will probably vary a lot from person to person. I would say I was a very straight forward applicant (paying for my own seat, trading my own money, us citizen, no outstanding debts), the process took me about a month start to finish. About a week for paperwork on my side including time spent mailing the app from California to Chicago, 2 weeks for them to process the application and answer any extra questions the exchange had, and a week to secure the seat and have my exchange fees reduced. For me, after the exchange approved my membership they emailed my clearing firm and the clearing firm reached out to a "seat broker" on my behalf to secure the proper seat and take care of paperwork.
Hope some of that is helpful.