Spray Tank Size?

I have 1.5 acres lot in South Florida most of which is St. Augustine. I am looking to buy a sprayer for my Toro Zero Turn to put down the normal assortment...fertilizer, pesticide, fungicide. Does anyone know what size tank I should be getting for this much lawn? Don't mind refilling once when doing the jobs but no more. What size tank should I be looking at? What are the acceptable go-to brands/models for this type of sprayer? Don't really know why but a sprayer is more inviting to me than a broadcast spreader. Is this a mistake? Thanks in advance for any comments or suggestions.....

If your doing just your yard I'd purchase a 15gal tank. Are you mounting tank on your ztr or pulling it on a trailer? If a trailer unit get the 25 gallon tank. Mine is 25 gallon but when its completely full it makes the front real light.

Thanks for taking the time to reply. I really appreciate the help. I have a Toro 48" ZTR and trying to decide on the best option. I could mount it I guess back or front or tow it. Just not sure what is best. I don't have a lot of manuveuring to do, some trees and inside corners but not too bad. I am still trying to determine whether spray or granular is best as well. Basically tired of paying $600-800 every quarter for lawn and landscape fertilizing and it still looks...eh. Bad fungus problem this summer and they responded slowly, inadequately, and with a bad attitude so 20% of my lawn is real bad and have smaller problems all over. I can do that myself!! So...trying to figure out what I need. Any hints on spray vs. granular REALLY appreciated...!!

Well I'd use granule fertilizer but you should take a few soil samples first. Contact your local department or agriculture for a soil probe and advice on what's best in your area. Fungus control can be obtained by liquid fungicides. This is a area pacific treatment what works here in east Texas may not work there.