Welcome to the forum and awesome shot!
The 50-135 is incredibly sharp, and many people here will say it's prime quality.
The Tamron 28-75 is also a very sharp lens, though a lot of people had problems with it--I had a very good copy, and it also focused pretty close.
I think the 16-50 is fantastic, but I've never been able to get great results at f/2.8. At f/4 or higher, it's very impressive.
However--will you be happy? Depends on how good you are at resisting the fantastic Pentax primes out there! I have both primes and zooms, and really don't want to limit myself to either/or. I had only primes for a while, then came back to zooms for the versatility and I've been very impressed with the image quality. But the primes are something else!
The FA limiteds (31, 43, 77) are definite favourites around here, their bokeh and sharpness are insanely good. Your personal roadmap sounds great, but if I were you, I'd consider the 50-135 in the long end and primes in the short end. The 50-135 is my largest lens at the moment though, so I usually bring the 77 when I'm not sure if I need the length.
The DA limiteds have an equally zealous following, though true, your 50 might preclude the need for a 40 and that's the most affordable.
The 31 is a fantastic lens, and if you can get one at a good price, it'll keep you happy for a while. However, it's not wide enough for everything. A good wide zoom, like the less expensive Tamron 17-50 can fill in a lot of blanks (and some say it's sharper wide open than the Pentax, but I've never had that Tamron). The difference between 31 and 17 is huge, and I decided that instead of buying 15, 21, 24, 28, 35, 40, 50, I'd try the 16-50 to complement the 31 and it works for me!
So, to recap--maybe get an excellent prime in a range you'd use a lot, then a zoom to complement. Or do what others here do, and buy them all