Whatever you frequency you decide, you need to ensure you are doing multiples of ie:
All of ours are 3 weekly - if this is too much for them the next option they have is 6 weekly, 9 weekly, 12 weekly when you're back in the area to do the 3 weeklys.
Some people wanted it 4 weekly or monthly and in the early days we provided for them. However as the business built we have learnt to our cost that having different rotas is impossible to stick to. You end up with having one week in 4 where you are trying to put 8 days work into 5
Don't let them dictate when they want it, if you do, you may find you are able to cope short term, but by the time you have built up a full rota you'll regret it. We have only recently managed to get everyone on a 3 weekly cycle.
Plus in an ideal world - 3 weekly equal 17.33 cleans per year - £17,333/year for every £1,000 worth of houses
Whereas on a 4 weekly clean you would only get maximum 13 cleans per year = £13,000 for every £1,000 worth of houses
Thats potentially £4,333 pa more, without the hassle of knocking on doors trying to get more work to keep you and your staff busy!!
Keep it simple and keep busy!