Ryan Air is a low cost carrier, very successful. You pay for everything, but let's face it, you do on many airlines now - including checking bags.
Since you work for an airline, I would advise taking an interline ticket on another carrier.

Paris is expensive and I live in London !

You have allocated very little time to really see very much. Paris can be accomplished in a couple of days, providing you're NOT going to actually enter any of the sites : I.e. see Notre Dame from the outside, Eiffel Tower etc.
The sites are well arranged in so much as being fairly close to each other. For the short time you are there, I would recommend buying a ticket on a site seeing bus and not getting off !

Madrid is a beautiful city too, compact.

As a 19 year old ....... What are you looking for - Straight bars/gay? Dance clubs?

If you're heading to Europe to Party, there are other cities that offer a lot more !