Help choosing lense for t3i

I am somewhat a beginner with photography.  I've been scouring the forums for reviews and input on lens selection.  What I've determined is that each photography style has a lense that works best/better than another.  There is no one "do it all" lense.  Problem I currently have is the salesman sold me a "do it all" lense when I purchased my t3i!  The guy is very knowledgeable and I feel was giving a noob what they wanted.  So, I'm not blaming him.  Now that I've expanded my knowledge base, I am realizing multiple lense's are the way to go.

I currently have a Tamron 18-270 3.5-6.3 PZD.  I primarily shoot outdoor - kid's sports, annual hiking trips in the mountains, dog playing, sunsets, Mardi Gras, etc.  I also pull the camera out on holidays, b'days etc., which is indoors.  In short, I am a novice photographer with an all around application.

My question and need for advice is whether to ditch the 18-270 and build a lense kit with at least two lense's covering the same range?  I am ready to pull the trigger on the Canon 70-200 f/4 L.  Sales guy thinks I should go for the f/2.8, but the bulk and weight don't seem reasonable for my annual hiking trips.  The other lense would be either a new Tamron 24- or Canon.  Or should I just keep the current Tamron, add the Canon L and disregard the overlap?

Last question.  It seems as though many professionals recommend and use fixed aperture lenses.  When does a variable aperture outweigh the fixed?  Reason I ask is for my wider angle lense selection, should I choose a variable or fixed?

Thanks for entertaining my noobness!