Boy, its already so late. I personally would say your odds of success are slim. They would probably grow, but you'd have trouble ripening a GOOD melon in the fall. One thing you could do if its an option is to install a plastic tunnel over them later on to trap the heat and extend the season -- that conceivably could work well, but you'd have to be extra vigilant against fungal diseases during the cooler fall weather. Really, though, I say you'd be better off just planting traditional fall crops -- collards, kale, cabbage, lettuce, snap/snow peas, daikons, that sort of thing, and save the melons for 2012.

Last year's cantaloupe produced tons of melons, it was a hybrid. This year I only got one melon and it was from a volunteer from last year's. The plant produced a lot less and the melon was a slightly different shape and a little larger. Seeds from an F1 are not likely to produce the same results as the parents. They usually revert to one or the other of the parent plants. As you go down in generations you get more likely to have the same results as the parent. If you had other melons in the same family odds are they crossed and you have seeds that will produce another first generation. Sometimes the desired results of the breeders comes at F2 so some hybrids seeds are F1 and some are later generations. Since we don't know the variety or what generation it was we really can't even guess what your results would be. You could save your seeds from your F1 hybrid, your F2 could be very different and if you saved the seeds from that your F3 could be different again. I don't know at what point in the generations they consider a hybrid to become open pollinated. Unless you did your own unintentional cross pollination an open pollinated plant will breed true. Many of the heirloom varieties are old seed catalog inventions and the original stories of the seeds being handed down from generation to generation were the biggest invention about them. I prefer the flavor of open pollinated varieties for everything but corn and I like saving seeds. With melons I get more reliable results with hybrids so even though I want the flavor of OP I'd rather have melons. If you wanted to save the seeds and still get results, plant one vine of your saved seeds next year and see how it does. If you like the results the year after only plant the seeds from your original saving. If you just want to be a seed saver you would save yourself some years if you started out with OP varieties.

That depends on how/where you plan to store them. If you can keep them cool and dry, you can buy them now, but if it gets hot and/or humid, you'll lose germination.

Buying seed off the rack is usually cheaper than from catalogs. Go ahead and buy them when you see them. Most perennials will be quite happy to be sown anytime before July and planted in the garden by fall. I've started many perennials during early summer. Some were planted in their permanent spots by fall and others spent the winter in pint to quart sized pots that were set in a trench and covered with leaves in the fall. Perennials are easier than you think. (that's why they live year after year)