I read in another discussion that 'molto' was used for countable things such as books, etc. and 'tanto' was used for uncountable things such as water and...beer. So is there a difference or no?
There is no difference, you can say both "tanta birra" and "molta birra". Tanto and molto are synonyms.
I seem to remember coming across this same point, between countable and non-countable things too!
But here is how Collins grammar describes things.
Tanto - so much
Troppo - too much
All adjectives, but also Molto can be used to mean 'very' to stress an adjective. So 'una bella casa' means a nice house. But 'una casa molto bella' means a very nice house. [Note when molto is used it goes with the adjective, after the noun!]
You can count bottles of beer. On the wall, in my stomach or anywhere else!