Many nouns can be used as both countable and non-countable. In three of the examples you give there are nouns that are nouns that are completely normal as countable nouns: "a success", "a journey", and "a tour". In the case of journey and tour they most often used as countable nouns, with regular plurals. In fact I can't think of a natural expression in which they are clearly non-count nouns.
The word "success" can be both count and non-count.
Success was easy for him (non count) / Day 3 was a success (count)
"A success" means "A successful event or time period"
Example number 3 is slightly different. It uses the phrase "a lot of..." ("hell" is merely emphatic and it should perhaps be "a hell of a lot of
stuff") here is is actually the noun "lot" that is countable. But this is now an idiom, and works with both plural count nouns, and non-count nouns
A lot of peas / A lot of rice.
Similarly "a hell of something" is also idiomatic, and in this idiom "hell" is a countable noun.
From the comments "A great pleasure" is like "a success", except that the count form of pleasure is less common, and mostly used in this kind of conversational expression. However you can say "A good night's sleep is one of life's pleasures." (from wiktionary)