pastorom

I just applied for the N-400 online yesterday (my first day of eligibility). Estimated completion time (this seems to be a new field, since i don't see it for my I-751 applications) is showing Sept 2019 (19 months!!!!)
Ugh.
 
As far as the process itself, very straightforward, and i actually much prefer this to the paper based application because i was always unsure there whether to leave certain fields blank or marked N/A etc. 
Also being able to upload all my docs (which are scanned already) was so much better than a large stack of printouts. Also, i remember during my I-751 application process (June 2017) there were people on the group for whom USCIS claimed they didn't receive their packets etc, and there's no way the Post Office can eff up here.
 
Just my $0.02.

Because they got the I-551 stamp in May 2018. The GC expiration has no relevance the moment you get your passport stamped. If they hadn't lost their GC, and gotten it stamped in Aug 2018, the I-551 would expire in Aug 2019. 

Mine too! Pretty stoked because now at least the application is fine and in the system!

1) Yes.
2) Yes.
3) No.
4) It's free so you may as well, even if you don't use it. It also has the advantage that you can work for any employer, not just the one you are authorised for on your H-1B.
5) I don't think you are obligated to tell them anything.