If you've looked at MSE, their Money Makeover tells you everything you need to know, eg reducing expenses and making debt as cheap as possible.
For your DHs overtime, I'd discount it from the initial budget and then when it comes in, use it to make extra payments towards your debts. When the debts are paid off, it can get added to savings and/or pay for an extra treat, depending on how your savings are looking.
For your income, work on a low average figure, and again, if you have extra money, pay towards debt, savings, or treats, in that order. Maybe get your income paid into a separate account and then set up a standing order to pay yourself a regular monthly 'wage' to even out the peaks and troughs.
Another top tip is to make sure you account for irregular and unpredictable expenses. You need to put aside money each month to pay for insurances, Christmas, holidays, and anything that breaks, whether it is a car, household item, or vet expenses if you have pets.
Many people say that they are 'short this month due to an unexpected car bill' but what they really mean is that they failed to save for car repairs, which are very likely to happen sooner or later and spent the money on something else instead.