I have 4 kids too - Son of (almost) 6, daughter of 3.5 and twins of 6 months. We have no family near us, my son started school 3 days before the twins were born, I had an emergency section and we live in a rural town where it is necessary to drive to be able to get to school and shops etc...
My aunt came and stayed with us Mon-Fri for the first 4 weeks. To be honest, we couldn't have coped without her, but that was because of our specific circumstances - I was in hospital for 5 days, the twins then had to stay in for a further 10 days in NN, we live a half hour drive from the hospital (on a good day) and even when we all got home, I still couldn't drive as I was recovering from the section.
I was driving at 3.5 weeks though and so my aunt stopped coming up (she lives a 4.5 hour drive away) and we coped on our own. My son has always got to school on time, with a clean uniform on and with his homework done. I can honestly say this is one of my proudest achievements!!!
So what helped us...? We had friends who cooked meals for us for the first few weeks. (actually my aunt cooked while she was here and then we used the meals people had made us after she's gone) I also had cooked chilli, spag bol, chicken stew, soup etc... and filled the freezer to the brim!!!
I also stocked up on essentials before the birth because our Tesco only has 2 double baby seat trolleys and they are more often than not hidden at the back behind 50 other trolleys and so I usually just put the girls in the buggy to shop, but obviously that means I can only pick up a small amount of stuff. It makes shopping hard and I have now given in and started used Tesco Home Delivery. We stocked up on things like kitchen roll, sandwich bags, loo roll etc... as well as staple food and baby items. Dashing out the shops for 1 or 2 things becomes a big deal with 4 kids so I loved not having to do it.
Having a positive attitude is probably the best you can do for yourself. I was also told I wouldn't cope and would need help etc... but do you know what - you do cope - because you have to! If I hadn't have had a section and the girls hadn't have been in NN, we could have coped without my aunt. It was great she was able to help us, but in different circumstances we'd have been OK on our own. If you believe you can do it, take each day as a fresh start and learn the mantra "This too shall pass", you'll be fine!!!
I would also say that with 4 kids and no help that a routine is a must! I know that for some people that's just a big no-no, but I have found that if I didn't have a routine then my son would never get to school on time, my daughter would never get to her gym class and no-one would ever get fed!!! I used GF, but adapted it to suit me.
My girls are FF because they have a dairy intolerence so are on prescribed formula. I had intended to mix-feed though and I fully believe it would have been possible!