Ted is right. Plastic tanks are the cheapest part of the sprayer. You may outgrow it soon, and have to buy a 200 gal unit in about 2 years. Also you will need a longer hose--300 feet not 150. And if your reel will only hold 150--then you need to spend $800 for a new reel. The ability to agitate the solution will be helpful--bypass part of the pump output. The Hypro 6 gal per minute diaphragm pump is about right. I think that would be the GR252. five or 6 hp motor is about right.
You may need to devise a roller system under the skid to allow you to roll it out of the truck onto a picnic table. Probably need a boat winch or come-along to pull it back and forth.
You can fill it only to 50 gals, if you want for your first year. If you have a light duty truck--it may make sense to upgrade to a 3/4 ton truck.