I painted my kitchen countertops with stone spray and made it look granite like. In your case you could paint it and do your sponge painting. Then I poured envirotex resin on top of it. You might want to make a frame for the sides of the countertop because the edges are tricky to get a smooth finish. But whatever you do, cover the lower cabinets with plastic because when it gets poured, it will drip down off the sides. Follow the directions on the box and you will love the result. For a few years after we did it, people thought it was real granite. Good Luck! Then you use a blow torch to get all the bubbles out. Google tutorials. It's a great product and our countertops have held up for years now. I think we used 5-6 boxes of envirotex for our countertops. Totalling around $300. hope this helps. It definitely has extended our old pink laminate countertops for another 5-6 years before we can afford real granite or quartz. Good Luck!
Both Rustoleum and Giani make kits that take you through step by step.
As temp measures either of the above will do. But if you want to use a sponged design, I suggest it is done in a press on and take off method and seal well when desired effect is achieved.
Here is a hometalk link for diy countertop painting.
Additionally - Here is an idea that I find exciting and interesting for your consideration. I hope this helps.