I once had some commercial equipment removed from a cafeteria. After seeing the 1/4-3/8 inch thick grease buildup on the sides of the fryer, my appetite for fried foods disappeared for a time. We actually started by scraping with a 2 inch putty knife. Then, we tried everything we could find. For places you could cover, we sprayed with oven cleaner and covered with plastic which was the method used for the company's candy production equipment. They sprayed everything on Friday night and let it sit for the weekend and cleaned it on Monday. The best product I have ever found was "grease control" from the Odo-ban company which is actually an emulsifier so much more green than the toxic chemicals found in some of the cleaners.

Fungus? Like mold? If so, perhaps try bleach, or taking out the wood and using something else. Fungus/mold in a restaurant is definitely not a good thing.

I just had mold removal on my new house because the contractor decided it was a good idea to wait until the end to put down plastic. They had to spray the mold and wire brush it. Then they treated the wood and sanded it. It wasn't a cheap job. It may be easiest and cheapest to start anew. I also recommend sinking the screws and filling the holes.

The wood has to reach what's called Equilibrium Moisture Content (EMC), which is different for various areas of the country/world. I don't know about end grain slabs, which is what you have, but the rule of thumb for lumber air drying (vs. kiln drying) is 1 year for each inch of thickness. Moisture leaves the end grain faster than the side and/or edge of the boards, so in your case the drying time will probably be shorter. If it is not dried in a controlled environment your slabs are going to split radially, due to drying too fast.