Hi, I have used Liquid Light and Rollei. Liquid light used to not be so great but they improved it when they did away with a premium option named AG+. They all behave the same way coating-wise. You may be deeper blacks with the Rollei. I used a bunch on glass and the darks never really got that dark. They say you can apply two coats but then it takes a long time to fix. You don't have to coat the paper with gelatin first but it will absorb less emulsion if you don't. I used to coat on fabric and it turned out but soaked up a ton. I'm about to coat black paper and am researching how to size, that's why I'm nosing around here.
Pro tips: Only melt what emulsion you are going to use as every time you heat it, you increase risk of fogging. Don't heat emulsion higher than 120 degrees F, 115 is good. Use a double boiler type of set up - make sure the heating element does not directly touch the bottom of the vessel that contains the emulsion because that zone of contact will end up being hotter than 120 degrees. Don't have the safelight too close. Have air circulation when drying and make sure there is no safelight or any light leaks into the drying area during the hours of drying. 
When I am about to coat, I cut open the whole plastic container and cut off what I think I'll need. You can try to dig it out of the wider containers, but not the tall Liquid light one. I store the rest in a metal reel tank with lid, in the fridge, taped shut with a sign on it to keep curious people away.
Coating on paper or fabric is the easiest way to get started. Probably sizing will be best. I usually do glass and metal which are more challenging. Good luck!
@seanphotoart on instagram if you are curious