1. What is used to fill the holes in the slate after the screws are put in?
I would suggest using an all natural bees wax. Bees wax has a very high melting point so it will dry very hard after being melted by a torch. Some people use plaster-of-paris. It will not shrink while its curing and it dries fast when mixed with warm water. The only downside is its very messy and can be a pain to get off if you ever have your slate releveled or move. I have seen people use all types of fillers for the seams and holes but the two listed would be the only thing I suggest. The application of both isnt as easy as it sounds. It may take some practice to perfect it.
2. What exactly is the Uniliner that Olhausen refers to? And is the slate backed completely in the construction?
The Uni-liner is basically a laminated piece of poplar-ply that will hit every load bearing point between the slate framing and the cabinet. Its a very ingenious design but adds a tremendous amount of strength to the table. It helps spread the weight out over a larger area. Its the same idea as putting a piece of plywood on an old roof so while your on it you dont fall through. Roofers use this all the time. As for the slate being backed completely...No it isnt backed completely. Its not needed on every point of the underside of the slate, only at the load bearing points and the edges. The framing on the Grand Champ is poplar which is an excellent hardwood for slate framing. Poplar has a natural self healing ability, meaning that after a staple is pulled out it will kind of fill the void where the staple once was.
3. Can the materials you mentioned stand up to the high humidity of the tropics?
To answer your question truthfully... I dont know??? I have never had a customer that was in a tropical enviroment. I live in Ohio which is a Mid-Western state that is known for its variations in atmospheric conditions. We havent had any problems that Im aware of on any of the Olhausen tables. I think mainly because they use very rigid straight grain wood that is kiln dried and monitered over a period of time before coating it with any sealants or finishes. The majority of the wood used on your table will have a sealant coat to prevent any moisture intake that may cause the wood to expand or contract. The only raw materials that will be exposed on your table will be the slate liner(framing) and the very bottom edge of your aprons. All of the remaining wood will be coated with a sealant. I dont see this table giving you any problems as long as the installation is done correctly. The installation will definetly make or break the table.
4. What is the most difficult thing to look out for in setting up the table?
The most crucial part in a good functional table will be the leveling. Not only under the legs but the slate must be leveled individualy to achieve a perfectly level playing surface. Cosmeticaly the most crucial part is the installation of the cloth on both the bed and the rails. Again its not as easy as it sounds. It took me 5+ years to learn the correct way to apply the cloth to the bed. The rails are tricky but not near as tricky as the bed. Did you get Simonis? If you did you have to call me before you or anyone else puts it on the table. There are a few tricks I have learned when applying Simonis on the bed and rails.
Hopefully this helps.