To me, getting the Tamron 17-50 is like getting the 18-135 without the additional zoom. My philosophy has always been cover your range with zooms, fill specialty areas with primes. The 18-135 can do bokeh if you're close enough to the subject... it's not its strength but it can do it. I thought I might like the Tamron 17-50 2.8 but realistically it doesn't give me much more than the 18-135. Which if you have one lens is really a no brainer. I can't imagine starting off my camera life with nothing to reach past 50mm. The 18-135 is quite comfortable being the only zoom you own.
(P.S. ha ha, I found the Tamron 17-50 on line, new for $389 and ordered it. I'm looking forward to it's across the board sharpness, especially at 17 mm, where I don't really have a good lens. I still would get the 18-135 first though.)
And adding a relatively cheap plastic fantastic 35mm 2.4 and getting started on your prime collection would be the way I'd go. I recently made a similar decision... deciding to go with a K-5 and a new lens, in my case the Sigma 8-16 instead of a K-5 II.
35 2.4 and bokeh.