Welcome to Pond Boss, Rachael!

We have lots of poison ivy at our place. Crossbow Concentrate is by far the best product I have used for PI. I can buy it at a steeply discounted rate from our County Noxious Weed Dept. (Don't know if you have that in Texas?) I do add a little surfactant because our poison ivy sometimes has a little waxy oil coating on the leaves and the surfactant makes your kill rate very high, even when the PI is waxy.

Greenbrier can be controlled with glyphosate, but well-established vines will probably require re-treatment. You should be able to buy RoundUp concentrate at a big box hardware store for less than the cost of Crossbow. There are multiple species of greenbrier, and some are VERY waxy. Make sure you get the concentrate with surfactant mixed in, or add your own surfactant (especially if you buy some for your Crossbow).

The glyphosate should kill the greenbrier way back, but it has running roots. A few of these will probably survive - even if you treated the plant perfectly the first time. When the re-growth sprouts up to 6" with broad leaves, then hit it again!

Is anyone in your family moderately handy with a chainsaw?

Cedar trees are generally easy to kill. Usually, if you cut the trunk below the lowest branch, then the tree will die.

Hackberry trees are harder to kill. Usually you have to poison the cut stump right after felling the tree for the best results. However, hackberry makes decent firewood. If you have a family friend or neighbor that heats with firewood, they might cut your hackberry trees for free? However, you must use a person that you trust. Felling trees can be a hazardous job. You don't want an idiot on your property that drops a tree on himself and then sues you!

Clearing trees is a big job! I would recommend making a small clearing first. Once the surrounding trees will all fall away from your clearing, then you can start planting your new trees. A little windbreak (in Waco!) from some existing trees will probably be a net benefit to your new trees - even if the existing trees cast a little shade.

Finally, I would certainly buy some of the excellent Pond Boss books. If you are knowledgeable yourself, then it is tougher to get scammed by a contractor or make an expensive mistake yourself. For example, all of my daughters wanted to be informed about car repairs, so they know if the guy in the shop is feeding them some BS!