Suica is good everywhere these days. You can even use it on the airport bus to Yokohama from Haneda—but I don't know if they sell Suica at the airport and I probably wouldn't bother to try to find one.

I live in central Yokohama and from HND, I'd never take anything but the airport bus to Yokohama Station. They run frequently and it usually takes less than 25 minutes and involves very little walking from past customs. You can buy tickets at the machine down on the platform where you wait for the bus.

Most buses go straight to Yokohama City Air Terminal (YCAT). Some stop first at the West Entrance to the JR Yokohama Station, which is the side the Sheraton is on. You need to tell them where you're getting out when you give them your bag so they put it in the right compartment under the bus.

YCAT is on the opposite side of the station from the Sheraton. I've seen visitors take a taxi from there to the Sheraton to avoid having to navigate their way through Yokohama Station, which is quite complicated. I'd walk, but maybe not if I was tired and had lots of bags and didn't have my bearings. (Getting your phone to correctly position you on a map as you go underground to get around the station isn't the easiest.)

Have fun!