Is it worth growing seeds, or shall I buy the plants?
How often should I water them on a week of 80+ temperature?
I can only say that I have read that they are not too difficult to grow from seeds. As for watering, that's really tricky, but the adult plants need very little water most of the time. I would not even water them once a week. To sprout the seeds, you'd have to get specific info from the supplier, but most likely it would tell you to keep the soil slightly moist, definitely not soggy. You might try putting them on a ball of damp cotton and sealing it in a plastic bag or container
I really do not recommend a novice try growing them from seed, especially if you are in a climate that is at all humid. I do live in a humid climate and have a great deal of trouble growing any of the mesembs from seed except Faucaria. You may want to ask this question in the forum Cacti and Succulents.