Replacing the T with a space is explicitly allowed by ISO 8601 if context makes it obvious that the date and time belong together. I prefer the version with space for many purposes since it's easier for humans to parse at a glance.

You are correct that time offsets are used instead of timezone names. The most obvious reason for that is that many names are ambigious (EST is either UTC-5 or UTC+2, depending on whether you live around the US or around Egypt).

Point of pedantry: RFC 3339 allows replacement of the T with a space; ISO 8601 merely allows its omission (and that only by mutual agreement of all parties to the information exchange).