1. It's grammatically accurate to say "how many clothes," but I don't think it's the most natural way to say it. Even though it's plural, we treat it like a "mass noun" referring to the general concept of fabric that you wear to cover your body (i.e. clothing), so it doesn't work well for the idea of individual articles of clothing. I would probably say "how much clothing" ("clothing" is uncountable). You could also say "I wonder how many jackets I should wear" or "I wonder how many layers I should wear." (a "layer" would basically be an individual article of clothing, such as a sweater, jacket or pair of long underwear, worn under or over another article. You would say this if you didn't want to specify the exact kind of clothing you were talking about, such as a jacket, pair of pants, etc.) 2. "Too many clothes" is grammatically accurate, but again, I would probably say "too much clothing" or "too many layers." (See more about "clothes" vs. "clothing" here: https://english.stackexchange.com/questions/202150/the-grammar-of-clothes-versus-clothing )

I think in general conversation you might say 'I wonder what I should wear?' rather than quantifying the number of clothes - this does not sound natural to me, and is not specific about the type of clothes you are wearing. Similarly, I would be more specific in the heat: 'I shouldn't be wearing a coat/scarf/jumper, it's too hot.' More often I've heard 'I'm wearing too many layers' when the person is feeling too hot.