Congrats on the promotion!

We had a cleaning service a few years ago, when DH was on the road all the time and I was recovering from my broken back. It was so nice to be able to come home to a clean home. What cleaning we did do was more of the de-cluttering/organizing type, and we left the deep-cleaning to the cleaning service.

To answer your questions:
1) we tipped during the holidays
2) every other week
3) they would do some minor picking up. They were not supposed to do dishes but if we had a couple things in the sink they would do them anyway. It was supposed to cost extra to have them do dishes, fold laundry, etc.

What they are expected to do should be clearly spelled out in your contract/service agreement.

One tip, if you have anything fragile around I would put it away. I had a delicate glass figurine that I had brought back from Murano, that got a few limbs amputated by the vacuum cleaner.