Hello, and I need help big time!  Beginner of the beginners

Hello, and I need help big time! Beginner of the beginners

Hi there, my name is Tetsuko, and I live in Round Rock, TX. This is in central texas. Intro wise, I am your typical working stiff pushing 30 whose passions lately have become everything house-related. Now onto the topic of gardening, I have the worst success with plants, seriously. I try to read up, but often feel overwhelmed. I am also a new homeowner. My husband and I recently closed on a house. It is new construction. The little landscaping shrubs they provided barely covered a single section of our yard. So we went to a local nursery, with check in hand, and purchased some shrubs/plants with recommendations from someone who worked there and seemed really knowledgable. She chose for us, 30 gals of pittesporum, waxleaf ligustrum, pampas grass (1), yucca (spanish bayonet), lantana, mexican heather, oleander (3) and texas sage (2). They planted them in the ground for us, along with a huge sago palm. These plants were chosen for their ability to withstand pretty bad heat, exaserbated by our friend laying down a black tarp to keep out the weeds and then some dirt (we later find out that this is actually a bad thing because it cooks the plants, so the woman at the nursery suggested the hardiest ones that she knew of). The three oleanders are planted without the tarp, as is the sago, but the others are planted in a bed, surrounded by the tarp, which is covered by dirt. I am totally unsure of how to water them, and how much. I got them four-five days ago, and I think I am killing them. The sago has soem brown tips and 80% of its leaves have a yellow tint in the middle. The leaf isn't wilting or anything, but the leaf is supposed to be green, right? He got watered (for about ten minutes, hose dripping water into ground) yesterday after no water for three days because I was told he likes it dry. The ligustrums are getting watered 5 mins every other day, as are the sages and everything else. I leave the hose and allow a steady stream of water to flow in for about 5-10 mins. The Pittosporum, while showing new growth, is also showing yellow leaves in the middle and here and there on the bottom and some leaf drop. The Lantana seems rather brittle. Please help! I spent like $500 and i really want them to survive. Please give me tips. I am a total beginner, I don't know anything about landscaping. All I want is something nice and pretty for the house. Am I overwatering? under? Every day lately has been close to 100 degrees. Our soil I believe is clay-like. Though the nursery people when they planted them, should have created proper drainage and stuff, right? Thank you so much!!
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