Just confused about where to start

Hello all,

I'm looking to add speakers to my audiophile setup which currently consists of (very high end) headphones. I want speakers for everything the headphones cannot do - simple enough. Problem is, I'm having difficulty deciding which gear I want to buy. I demoed a pair of B&W 705 S2's today and was very impressed. Unfortunately, my budget isn't that high. It's $1500 total, for the speakers and amp combined. Source is a computer. I listened to a cheaper pair of B&W bookshelf speakers (can't remember which, but were around $1200) and was not impressed. I am leaning toward bookshelf speakers but don't know if getting floorstanding at this price point would be a large increase in quality. The room they will be placed in is only 100 square feet. I am willing to buy used.

So, my questions, summed up are:

Is bookshelf a better option than floorstanding?

Is it worth looking at cheaper B&W models, or should I look at other companies altogether?

At least with headphones, I like a pretty neutral sound, if not a tad warm. Are there any companies that predominantly have this sound signature?

How should the room size inform my choice of speakers?

@jond hmm...so I don't need a beefy 300w power amp then? I'm afraid I'll underpower the speakers so that they can't be cranked when need be.
Trust me 300 watts are not needed just get the best watts you can on your budget! Look for amps with robust power supplies over bit wattage ratings.
That room is tiny, so you really do not need massive amplification. Spend as litle as you can on the amplifier (within reason) to have as much budget for speakers.
Can you use your headphone DAC/amplifier as a pre amplifier? If you can, you will only need a (modest) power amplifier.
You do run a risk with second hand speakers. They may have been abused, and they may have degraded. Many do not perform to spec anymore after only 15 years, or less if they have been in the sun in front of a window.
To elaborate on the room size issue: the Schroeder frequency of that room will be about 275 Hz. Below that you will suffer room modes (i.e. massive peaks and dips and hence boomy one note bass), and the more so the more deep bass you pump into the room. Hence my preference for speakers without deep bass. The bass that there is will still have to be corrected/equalized. Since you will be using a computer as a source, this is relatively easy. All you need is a cheap UMIK-1 calibrated microphone, using the free REW software. Measure the in-room response (you will be horrified), create a correction curve, and load that into the free Equalizer APO software (if you are using a PC, there are alternatives for other platforms).
  Man if it was me all I want to do in any price range , especially yours is wait for something great under the money to come along. My choice however would be especially based on your comments to look for a pr of lightly used Magnaplanar MG II,s for around $800 or so. On EBay right now is one of the biggest baddest best sounding underrated bullet proof integrated amps around. Sansui  Aud11 for $700 that would make some Maggy’s very happy with its 200 w x 2 huge power supply and just as happy into 4ohms 
 Sold a lot of better audio in my early days and always thought this amp sounded as good as a lot of other gear costing 3x the $
 bookshelves can sound great but nothing better at modest volumes than Maggie’s ,they get up and follow you around.
 Good luck.