Congratulations!
I have had an emergency section with epidural after 36 hour labour wuth my first and an elective with spinal (no idea what the difference is!) with my second (13 months later) Elective section is absolutely fine - very relaxed. I arrived at hospital at 7am - when down to theatre around 7.30 ish and was back on the ward by 9.30am Left hospital after 2 days. You may be able to have a normal birth anyway, i am sure that they will keep a close eye on you, but if it needs to be another section, I wouldn't worry too much.
As for when to tell the older one, i never realy had that issue with mine being so close in age. I agree though that time does pass very slowly. Bear in mind that it will be about a quarter of your sons life that he will have to wait, so probably better later than sooner. He will however probably hear you talking to other people about it pretty soon and is old enough to know that something is happening.