@outlander, a hint with seedling punnets- the biggest plants are not always the best ones. Sometimes they've been in the punnet for too long, and the roots have gotten crowded and tangled. If you've got a choice between punnets with tiny plants/medium plants/tall plants, go for the medium ones. The tiny ones may be too little and not have the root system they need to survive.
Also, if possible, don't buy punnets which have plants already in flower. They look enticing, but once a plant starts flowering, it's chemistry switches into "flower, set seed, die". Most seedling flowers only have a one year life cycle, so the plants are genetically programmed to produce the next generation. If you get plants that aren't flowering yet, they'll be better at putting roots out into their new home. The "instant colour" pots that nurseries sell are really only good if you need to fill out a garden in a hurry, and for a short time. Within a few weeks, they're past their best.
If you can, hold off on planting until you get a couple of cooler days. Being summer that may not be possible, so if not, then keep the pot shaded for the first 2-3 days, and don't let it dry out. The soil should be about as wet as a damp facewasher. Totally soggy and waterlogged isn't good. Light watering twice a day (until the water just starts to come out of the drainage holes) will be good for getting them started, after that once every day or two should be right, unless it's heatwave weather.
