I used Viator for shared shuttle from airport for $25 US -we hit traffic so longer than train option. I did a great street art tour from underground tours (review on my blog philatravelgirl) -agree w/others high tourist season and lines so buy Eiffel ticket online and then IMO walk everywhere stop at a cafe and get some macaroons. Focus on one-two musts - the Louvre does an English tour of the highlights if you must but I'd be outside walking.