Today, I learned new expressions: through thick and thin, come thick and fast, not too ostentationus, throw the kitchen sink at, wouldn't hurt a fly, and set a foot in/on. Today, I learned new expressions: through thick and thin, come thick and fast, not too ostentatious, throw the kitchen sink at, wouldn't hurt a fly, and set a foot in/on.

I'm not sure if "not too ostentatious" is an idiom, it seems like a normal sentence to me. The others are all good though.

Today, I learned some new expressions: through thick and thin, come thick and fast, not too ostentationus, throw the kitchen sink at, wouldn't hurt a fly, and set a foot in/on. Today, I learned some new expressions: through thick and thin, come thick and fast, not too ostentatious, throw the kitchen sink at, wouldn't hurt a fly, and set a foot in/on.

The more time I spend time learning English, the more English expressions I feel that I have to learn. The more time I spend learning English, the more expressions I feel I have to learn.

What you had was ok, but putting time earlier in the sentence flows better to me. Also shortening the second part makes it sound a lot better.

The more time that I spend time learning English, the more English expressions I feel that I have to learn. The more time that I spend learning English, the more expressions I feel I have to learn.