How do you use Berryman B-12?

[Weekend Rider]

First Post: As a newbie to this forum, just reading, learning and being amazed at the wealth of information here, I'm blown away!

I've recently bought a 2001 GZ250 with 3,700 miles on it. I've only ridden it on a very short test ride due to the cold weather. It was sitting unused for a few years and I suspect it has some carb issues and needs to be cleaned. A post from a user I cannot recall stated pouring Berryman's B-12 or Seafoam into the carb and let it soak overnight. Or is just using it as a gas additive is the extent of its use?

Am I correct in thinking I should remove the carb and let it sit covered with the B-12 overnight to clean the probable gunk inside?

The bike is hard starting and runs a bit rough with flat spots. A new plug (Denso X24ESR-U), air filter (Hi-Flow), oil filter, Shell Rotella-T oil and other goodies are on order. I suspect this bike was just ridden and not cared for properly but is in fairly good shape cosmetically.

Any other issues I should be concerned about for a bike this old and not ridden that much?

Living in Pennsylvania there will be no riding till spring. Winter will give me plenty of time to get it in shape.

I'm happy to have found a site dedicated to this bike with the wealth of knowledge and so many helpful folks. It's great and just what I needed. Thank you.