Speakers to Invest In?

Background:
I just got my first 2 gigs earlier this summer in the Chicago suburbs. I recently moved into Chicago proper and am looking to get gigs on the weekends to take the financial pressure off school. I intend to make DJing a regular part time job while in school. And the gigs I'm most likely to land, will not have any respectable sound system, if one at all, thus requiring me to bring all my own kit (and kaboodle).

My current kit consists of a Numark MixtrackPro, MF Classic, and Traktor. As for speakers, I have an old pair of 12in Stageworks and a 2ch amp (don't even know the wattage) on extended loan from a friend. At the dorms I practice on an old 2pc Aiwa home stereo, using the included speakers for mids/highs, and a pair of Bose 401s for the lows.

For the gigs I played out, I borrowed a pair of JBLs and a 2ch Gemini amp from a buddy.

Issue:
While that Aiwa/Bose hybrid setup I work on in the dorms gives fantastic sound quality, it's not something I can use to play out. It's not portable (read: durable), and doesn't look professional either; a professional appearance is something I'm very conscious of putting forth so that anybody who books me will treat me with respect, as well as anybody in the crowd who could potentially ask to book me in the future.

I was looking at guitar center (I still have a relationship with the guy who sold me my Numark who is also a fellow DJ), and am pretty lost as to which speakers to buy. As a student I'm not too keen on parting with my greenbacks, but an engineering internship this summer did help, making my budget a little better. If I go the pricey/pricier route, I'd like those speakers to be good ones that will last -an investment, if you will.

I was told by that guy at GC, after explaining to him my situation and exp, that I should probably just stick to a pair of powered speakers -though no smaller than 15".

He suggested a pair of these 15" powered Mackie speakers.

These 15in Peavey speakers also caught my eye for the same price as the above Mackie model.

Lastly, on the high/pricey end, I ran across these dual 15in Peavey speakers. I'm posting these here cause I'm concerned about having enough bass (people wanna feel the beat/groove). And these, of course, at their price, would definitely be a long term investment. After hitting up the local bar last week, and seeing the DJ there with a pair of these, a light setup, AND a pair of subs, I felt extremely under geared (though on the flipside, I've seen guys play there with a pair of speakers on stands and some lights on stands too...).

Questions:
1) Other than there being one less piece of gear to lug and connect (amp), what are the pros/cons of powered vs. unpowered speaker setups? Is one actually better for mobile DJing than the other?

2) Do I really need 15in speakers, or will 12in do me fine?

3) What about sub(s)? Should I invest in one right now; go with small(er) speakers and sub(s)? If so, are they normally bought alone, for a sort of "2.1" setup, or in a matching pair for a "2.2" type arrangement?
3a) How would I plug said sub(s) into my setup? Do I need a dedicated amp to include a sub or can I connect sub(s) in tandem with powered speakers? Do they normally have pass-throughs for my mid/high speakers or can the pass-throughs on mid/high speakers work to send the lows to the subs w/o negatively impacting the signal?

4) Are those dual 15" Peavey speakers really worth it for a long term investment? And are they good enough in the bass department to forgo a sub(s), if they are worth it in the long run?

I'm not opposed to any store at all, though that guy I know at GC said he'd help me out on such a big purchase as a show of reward for my previous loyalty.

Thanks for slogging through this post guys. I'm a DJ just starting out and really wanna take this far, so any help is much appreciated!

If there's anything that needs to be clarified, ask away!