I have 5DC they're now 21,19,16,14 and 10.
Firstly Congratulations 
When I had 4DC I had become a single parent a few days before I found out that I was pregnant with my 4th DC and I was fine,it was actually really good,I managed alot better than I would ever have thought I would.
I worked part time and went to college once my youngest was 18 months old.
Best tips I can give is try not to panic
don't be to hard on yourself and try to not sweat the small stuff that and get organized the more organized you are the more chance you have of getting out of the house and getting to places on time.
The getting organized for me started when I was pregnant with my 4th,towards the end of the pregnancy I did lots and lots of cooking,so I batch cooked meals to go into the freezer that with a few roast dinners and easy pasta dishes that I'd make when they were needed would last for 3 months after my 4th was born.
Every school day once the DC were in bed I'd iron everyone's clothes for the next day and lay them out ready with they're underwear(including mine and the baby's clothes)I'd make sure that the DC school bags,P.E bags,the baby's bag were all ready the night before.
Every day they got in from school I'd make sure that coats were hung up and shoes put away so we didn't have a mad rush in the morning looking for a missing shoe or coat.
Taking them out I had a double buggy because there was only 20 months between DS now 16 and DD now 14.
I took them on holiday in the UK on my own for 10 days,we had days out to parks,museums,legoland,farms and zoos,it took a bit of planning but it was always worth it.
Honestly once you get into a routine you will be fine. 