Here in NC they say to seed around Labor day or after, so you should be good to go. One thing about dethatching though is if you already have fescue you really shouldn't need to do it unless you've had large areas that died and have thatch layers covering the ground. Otherwise, you're just gonna be pulling up good grass plants...not good. You might find the link helpful also. Here is a link that might be useful: linky

I've done that many times, don't worry, it's a normal symptom of Compulsive Horticultural Acquisition Disorder (CHAD). I would not recommend planting them outdoors just yet; as you mentioned, there will surely be some cold snaps. If you keep them indoors, you'll have a good jump on the growing season and may have nice-sized plants come spring. What works for me is to pot them up and keep them on a fairly cool windowsill until the ground is workable. I try to keep them in semi-shade for a few days after potting them, until their roots have gotten fully functional and the plants have recovered from their dormancy. I don't feed them, but otherwise treat them like houseplants. Through my own poor planning, my cool windowsills have all disappeared, so I can't give in to those bargains any more, but I bet your plants will do just fine.

I have an older 24" oven, and I've done some research in the event we have to replace it. Most of the 24" models are European brands, and certainly most with convection are European. In your price range, Fagor and Bosch are probably your best bets. Someone on the Appliance forum has a Fagor 24" oven, and there are some posts about it there. Bosch, of course, is more widely available. Neither of those will have temperature probes; for that, you would probably need to step up about $1,000 over your budget to Miele.

You will want both annuals and perennials. In Texas you will want to plant as many perennials in the fall so they have a chance to grow roots before the blast of summer heat. Otherwise you will be watering heavily your first season. The annual periwinkle will do great in the Texas sun and give that continuous splash of color you are expecting. They come in bold pinks and you could mix it with salvia, lavender, which have purple flowers. Remember that gardening is like working on an oil painting, you learn by doing and you sometimes change your mind and move things. You also will find that your yard has micro climates and some things may do better in some places whereas a few feet over the same plant wont flourish.