Most bathroom vanity basins/sinks are pre-drilled for 4" faucet sets. My guess is that the "optional" 6" deck is to cover these in which case it will fit your existing basin thus permitting the single hole faucet intallation. The instructions or packaging will confirm or advise if you must order one as a separate part.

In our house, all of the various bathroom sinks and showers have two handles, while the kitchen sink has a single lever. With two handles, changing the temperature of the combined water flow changes the volume, so it always takes a few more seconds of fiddling around to get everything right. On the other hand, the single lever is intuitive, faster, and only requires one hand. That's a definite advantage whether you have something in one of your hands -- like a toothbrush or bar of soap -- or not.

The most common 3 hole vanity top typically has a 4" distance between the outer holes. This dimension is measured from the center of one hole to the center of the other, thus the term centerset. That type of hole drilling needs a 4" center set faucet which would Something like this The other common spacing is often just called widespread, or 8" widespread. Widespread faucets look like this If the holes on your top are drilled for a 4" centerset faucet, I think the 2 extra holes might be too close to the single hole faucet for the soap and lotion dispenser. The plate to cover the holes is called an escutcheon. When we redid our bathroom we wanted an 8" widespread faucet but our plumber mistakenly told the fabricator we were using a 4" centerset. We didn't catch the mistake until the top was installed. I really dislike centerset faucets so the plumber offered to replace the countertop but we didn't want to waste it so we used an escutcheon and a single hole faucet instead. It's not what I preferred but it really doesn't look bad. Here's how it looks Hope you can figure out a good solution for vanity/faucet.

Just moved to a new house, replaced the old Moen faucet in the kitchen which was clearly never installed properly in the first place. I grabbed a Delta Owendale single-handle faucet from the Depot and went to install (I'm no expert but have done a few faucets in my time). For context, it's a double offset sink with two holes in the granite countertop, but due to the offset it won't work with the included escutcheon. I went for the single-handle installation and was confused that it didn't have any sort of gasket or other seal solution. The kit came with a "thin deck aid" which requires a three-hole configuration and did have some little gasket piece, but that piece didn't fit in the faucet when not using the deck aid. The Delta instructions are somewhat generic and from what I can tell don't really call for any gasket for single-hole install, using terms like "if your faucet has a trim ring" (unless I'm reading it wrong, which I could be). So I just did the install and tried it out - and of course it does leak when it gets splashed. I have called and emailed Delta multiple times but can't seem to reach anyone or get a reply. There was nothing in the box which would have worked as a gasket so maybe they just forgot to include it. In any case, I'm wondering where to go from here. Is there a generic gasket that I can use, or must I continue trying to reach Delta to get whatever part may have been missing from my box? Or should I just use some silicon sealant around the base and call it a day? Forgot to mention, there was also a soap dispenser which I installed in the hole that used to hold the Moen handle, just next to the faucet. It does have a foam gasket built in, but it also leaks. So I am thinking maybe a sealant would be the way to go regardless - if so I need recommendations for what product and how to apply it, as I've never done that before. Thanks in advance!