How do you choose components for a gps antenna
If I was doing this in one off or small volume I'd choose an RF chain that had the most chance of working with the minimum of effort.
That would almost certainly have antenna, RF amplifier if used and GPS IC integrated in a module that I connected power and basic signals to.
Even trying to implement a reference design with separate antenna + amplifier + GPS IC would be liable to be one to quite possibly two orders of magnitude harder.  (= 10 to 100 times harder.)
It may be small and look trivial, but antenna implementation can be demanding beyond reasonable belief. If meeting an extraordinary a challenge is not the aim then learning how to tame GHZ level RF is best left for another occasion - on each occasion when the need arises :-).
As for specs - I'd read spec sheets.
If a device did not have a good spec sheet I'd look for one that did have  - I'd buy a poor spec sheet device only if it was well known and recommended by a large community of users and if there were technically compelling reasons to do so.