Any programming language that allows one to use inline assembly would be as "limitless" as assembly language. Both C and C++ qualify in this respect.
1. Apart from Assembly, what language has the least limit in fuctionality. I would like if it was good in visual terms, but that's not the main feature I'm looking for. And is Assembly the most limitless language out there (I know it's very low-level).
The frequently repeated advice is to use the right tool for the job. As such, what is the job, and how familiar are you with the tools? Anything else would just result in endless discussions of language features/"misfeatures", libraries, programming idioms, etc.
2. Which one should I go for: C or C++? I know many ask this question and I've seen the answer, but I'll be more specific. Which one has less limits? Which one has more functionality? I've read a lot of information on the internet, but I still can't make my mind.