Hello!
The answer to most of your questions is: Depends on your farmer! With the actual birth: some farmers like to leave their ewes to it unless theres real problems, others get there hands in straight away to get the job done.
Ewes lamb day or night - and as to how many will lamb per day it depends on the farm - how many tups there were, when they were put with the ewes - probably an average of 5-6 a day with that kind of flock size.
When I go lambing my jobs include: taking the (pregnant) ewes in and out of the barn morning and night, feeding them, feeding and watering the ewes in the lambing pen who had there lambs a couple of days ago, docking and castrating 2 day old lambs, moving lambs and ewes into the field when they're old enough, drenching the ewes, bedding up and cleaning out lambing pens, bottle feeding orphans or trying to get them onto an adoptive ewe (which isn't easy), moving ewes and lambs inside to lambing pens if they gave birth in the field, and of course helping ewes who are clearly in trouble eg: head out, breach, back legs first, one leg only etc. After lambing a ewe it's common that you give it an antibiotic injection (I/M back of neck).
Think thats about it - if you go lambing, its likely you'll just be watching for the fist couple of days - the shepherd will want to get to know, and trust you. Make sure you do whatever he/she says, and do it well, then hopefully you can have a go at lambing by yourself!
oh, and finally, lambing is great, the best work experience I've done - do all you can to get work exp on a BIG sheep farm 400+ ewes. Theres more to do and it's even more fun!