How low is too low?

I'm on about 2000-3000 kj (500-750 kcal) per day at the moment. Am I going
to have any problems with this? I have a lot of weight to lose, so this is
something I'll have to be doing for months.

Last time I lost weight, I think I was doing 5000-7000 alternating day by
day. I plan to resume that after about 1-2 months, but to start off I'm
going super low just to kick start the weight loss and to get myself
disciplined.

Actually, last time I had trouble getting up my quotient of calories, ie.
forcing myself to eat when I wasn't really hungry. I figure if I can get by
on less than why bother? I don't want to have to do as much exercise as I
did back then (2-3 hours a day). I'm only planning on 30 mins to 1 hour this
time.

I think I'll try to have an extra meal every second day because that
alternating thing seemed to work for me last time.