You said you're out of money. I'm going to suggest some things that will cut your costs considerably and should develop a nice organic pasture for you. There will be costs involved, however. I'm going to suggest electric fencing, plastic troughs, grass and legume seeds, and chickens to help you cut your costs and develop the organic nature of your land. Probably your biggest bill now is supplemental feed (even if it is your own harvest), so these suggestions are heavy on your developing a way to cut that cost.
A good way to go organic in a grazing situation is to let nature's beneficial beasts start helping you out. Once you stop using herbicide, insecticide (including livestock wormers), and fungicide, your land will be on the way to taking care of itself. Your job will become the management of the animals so that they can all work together in harmony. You will have to throw some seeds, fertilize (but hopefully not much with nitrogen), and provide water to the livestock, but that is relatively easy to handle.
If you fence your horses and move them around on a schedule, they will do much of your work for you. They will harvest your grass (you can sell your haying equipment), spread manure (sell your manure spreader), and plant your seed (sell your seeder). Here's how. Fence your 16 acres into 16 pastures of 1 acre each with good electric fence (even the really good electric fence is cheap compared to wood or steel fences). Instead of the spring gates they recommend, use electric tape - it is visible enough and dirt cheap compared to a spring - especially when the spring gets stretched out 40 feet into the adjacent pasture. The gate will end up costing about a dollar instead of $15.
If you keep all the horses in a pasture for a week, it will be 15 weeks before the horses return to a pasture giving the grass a chance to regrow. Overgrazing is caused when the grass doesn't ever get a chance to rest and regrow. So having all these pastures will prevent overgrazing. Not only that, but when grasses grow tall, their roots grow deep. Then when the horse bites off the tall grass, the roots no longer have enough sugar coming in, so many of the roots die off. Those dead roots become the organic matter in your soil that is so very important to soil health. Then when you let the grass grow for another 15 weeks, the new roots will grow deep again. This is the fastest way to get organic matter deep into your soil.
You'll need water in each pasture. A 40-gallon Rubbermaid trough is good and portable when empty. Fill with a tough garden hose and a float valve. If you had two troughs, you could have the fresh one ready in the new pasture before you open the gate and then let the old one drain. You can locate the troughs where you need to churn up the soil to stimulate new growth.
Move the animals from pasture to pasture depending on when the grass in the next pasture is ready to eat. The horses should remain long enough to eat most of the grass in each pasture AND spread manure over the entire area. That will take care of your manure spreading. If you know what minerals the soil needs, you can put the minerals in the salt for the horses to spread that out for you, too.
Have you considered putting some different clovers in with the bermuda? Some clovers lush out early and some later. All clovers and legumes can inject nitrogen fertilizer into the soil for you. Or how about some delicious Johnson grass? Oats? Alfalfa? I have a problem with coastal, especially when it is pretty much a monoculture. Once it goes dormant, it's all over for that grass and that pasture - suddenly you have to pay for supplemental feed. That's why I'm suggesting some back up forage. You can buy a lot of seed for the price of a roll of hay. If you get the right mix of legumes and grasses, you should never have to apply nitrogen and you should have fresh, living forage all year long. If you throw the seed before the horses move into a pasture, their hooves will prepare the seed bed and push the seeds into the seed bed for you. Then they will fertilize if for you, too.
If you are using a wormer now, the worm medicine is likely killing off some of the soil's beneficial worms and even beetles under the horse's manure. This is a bad thing. You can avoid this by only giving the worming meds to horses that have worms. For the rest use diatomaceous earth in their mineral. That will minimize worms. The continual movement of the horses from pasture to pasture will keep them from spending a lot of time in their own manure and will help keep the pests down.
If you have horse manure piling up and not disappearing by itself in the pasture, you might bring in some free ranging chickens. They will eat the pests from the manure and spread it over a larger area. Even if you have to buy chicks, and the coyotes eat every one of them, they are worth having simply to spread manure around for you for very little cost and labor. Plus you might get some eggs out of the deal.
If you're going to Texas Plant and Soil Labs for a test, have them check your forage, too. This might be more important than having the soil tested. There can be conditions where the soil has the right elements in it but the plants aren't getting them. I would never suggest this to someone just growing a lawn, but your grass is forage. It has to be good. Texas Plant and Soil Labs specializes in this kind of plant testing.
If you do all this, you should only have to keep track of potassium, phosphorus, and trace elements. Just about everything else is included.
And I've found molasses for more like a dollar a gallon, not $8-$16. Look for a co-op where they buy it in huge bulk and sell it by the pound (you bring in your own containers). Cost is about $0.10 per pound and is subject to market conditions. A gallon weighs 10.5 pounds. You might spray every pasture with one gallon per acre after the animals leave it. Spray everything in the field to stimulate microbial activity.