I found 1 child very hard and quite frankly I'm surprised I had any more at all, nevermind 4!
Going from 1-2 was the most difficult for me, I left a 3 year gap between 2-3 to recover and then had no4 2 years later.
They're 7,6,3 and 1 and it is unbelievably difficult, however,
all mine are home as we Home Educate too.
My advice would be think very carefully about it because 'a picnic it is NOT!'
The house is constantly trashed, the washing pile is humongous ALL THE TIME, they absolutely outnumber you and they know it. You'll need a BIG house, not necessarily for the bedrooms, but for the amount of living space.
For instance;
a dining room table for 6 (noone ever mentions that)
toys for 4 kids (don't under estimate how much storage that takes)
Other things to note;
things like 4 bikes (where to put them)
uniforms/clubs for them all (costs and time spent ferrying small people about)
the cost of holidays/flights etc (you'll be hard pushed to get a room abroad big enough)
the big car to transport you all
the shopping bill, which has yet to dip under £140 per week, despite my very best efforts
childcare costs if you go to work
proximity of family to help out (mine aren't that close, but I really do wish they were)
Consider your age, the gaps you hope to have in between them, the toll of pg on your body (which got harder with each child due to SPD for me) and finally whether you can cope with the sleep deprivation, which generally lasts at least 8 years with 4 children ;)
Best of luck.... taking all the above into consideration I would still do it all again...I LOVE IT!! :D