How could I identify whether given RNA-seq data is paired end or single end
To find out whether a dataset was paired-end or single-end, go to SRA, click on a run, and look under "Library". Paired-end datasets will typically have "Layout: paired". Note that people don't always mark this correctly, which causes no end of headaches.

Regarding lines like "CCCFFFFFGFHHHGJJJJI#1?FEIGGI", that's the quality score line. Look at the fastq article in wikipedia for more details.

Edit: Regarding the updated portion of your question, no you can not increase this length. The sequences produced by Illumina machines are a fixed length and that length (or whatever length was submitted) is what you're getting. As a general rule, you'll get whatever sequence was updated (unless you forget the --split3 (or whatever it's called) option).