First off, well done on the ram lamb prices, those are very good.
Some of the answers are breed dependent, also climate dependent, so please tell us what breed(s) are your sheep and where are you?
Assuming for the moment you don't have all-year breeders, very fast maturers and aren't somewhere really warm, you are probably ok at this time of year leaving the ewe lambs with their dad for a couple of weeks at least - which is plenty of time to dry their mums off. Personally I would keep the ewe lambs away from the ram after that (assuming you are not planning to breed them this year.)
Flushing is optional; we avoid it as we are happier with good single lambs than smaller, slower-growing twins. If you want as many lambs as possible then yes put the ewes on really good going a week or two before introducing the ram. If you want the girls to lamb as close together as possible, it helps to run them with a teaser (usually a rig, ie, a ram whose testicle(s) are internal and whose sperm therefore is infertile) or failing that, in a smallish field with the ram next door so they can smell him, for 17 days or more before the ram goes in.
Especially if you have a lot of ewes for the ram, make sure he is in tip-top condition for the job - start about 7 or 8 weeks before you want him to work. It takes sperm 6 weeks to be produced, so the sperm that will fertilise your first lambs are being produced 6 weeks before the ram joins the ladies. Check him over and start feeding him before this - but don't get him fat. It will help him if you can feed him while he is working - usually the 6-8 week build-up gets him pretty tame and eating from a bucket you are holding.
If your ewes have worked hard, for instance rearing twins and triples without additional food, you maybe want to be thinking in terms of 2-3 months after weaning before they are tupped. If you have been feeding them, and/or they've been on very good ground, or they've mostly reared singles, then they'll need less time to recover and rebuild their condition.
In the run-up to your desired tupping date, monitor the ewes' condition using 'condition score'. Ewes should be fit but not fat going to the tup; a hill ewe condition score 2-2.5, a lowland ewe 2.5-3. (Basically you should be able to feel the vertebrae and ribs with a little pressure but there should be muscle either side of the vertebrae; it shouldn't be concave. 4 is fat, can't feel the vertebrae without quite a lot of pressure; 2 is slim, can feel the vertebrae easily.) It takes a minimum of two weeks to make an appreciable difference to condition score. So check them at least 6 weeks before tupping and seperate them into 'thin', 'fat' and 'fit'. Feed up the 'thin' and control input for the 'fat'. Check them every two weeks and take action if thin ewes are not improving.
For maximum lambs the ewe should be 'on a rising plane of nutrition', ie, her intake and condition should be increasing as she goes to the tup.
I hope that helps. Tell us a bit more about your situation and we can give more specific, less general advice.
Sally