Hi! I'm in Qatar and although I don't have kids yet, I have one on the way (due December).
I can try and answer some of your questions for you;
Schools - I would recommend contacting Park House and DESS first off. I know some of the teachers there and they are lovely people and enjoy working there and the kids seems bright too!
Accomodation - prices are on the increase, so I would recommend looking for a villa fairly quickly once you get here. Is your DH's company putting you up in the mean tmie?
Chances of local hire - good for a teacher, but I would stronly recommend you DON'T apply to Cambridge - everyone I know that's worked there has had an extremely rough time and left very very fast. Try Doha College and search online. Once you're here you'll get to hear of more schools and plenty of teachers as well. It's very much a case of not what you know, but who you know here.
Sailing Club - can't help on that one I'm afraid
Restrictive - not at all. As long as you dress sensibly you'll be just fine. Knees and shoulders are the minimum requirements.
Once you arrive and get settled, I'd recommend looking at joining Doha Mums (www.dohamums.com). It will be a great way for you and your girls to meet people.
For more information, you can also look at www.qatarliving.com. It can be negative, but don't let that dissuade you. It's more Qatar specific and a good way to find second hand cars and furniture if you need it.
If you need any more info, don't hesitate to ask!