Xiaobaotu and other nice buddies,please help me on I-765

I am holding a school job which is not secure, so i pan to apply for my EAD as back up since my 485 is pending. I have two questions:
1. my H1b is not used up, so I prefer to remain in my H1b status if, only if there is another school job available. If my EAD is approved, will it affect my H1b status? I assume that my application for H1b will do no harm to my H1B unless i have to use it. Please corerect me if i am wrong.

2. How long do you know it normally takes to get approval in Texas center?

3. I used OPT before after graduation, is it the same kind of EAD, should I report OPT on Question 11 Form 765, which asks: have you ever before applied for employment authorization from USCIS?

Thank you in advance!