The truth is that, as you have discovered, there is no data to canonically define which creatures you can select as familiar. Probably by design, the familiar is currently an undifferentiated set of statistics based on the player. This may change with the Gamemastery or Bestiary 2 guide, but I will not rely on it. In other words, a familiar follows the pattern described in the familiar section regardless of what they are – they have your backups and AC, 5 * your level damage, the tiny size, the vision in low light, and either a speed of movement or a swimming speed of 25 feet. Beyond that, it is an animal (restricted to small animals), unless otherwise indicated by the function that gives you the familiar picture (such as the druid's lehy). As you said, it's the base, and the animal you choose is little more than a dressed ensemble.
I think the obvious intention of the designers was not to make one pet intrinsically better than another – "oh, I'm going to bat because he's blind-eyed and flight "or" I'll take the spider monkey because it has hands ", etc. So, all pets go on an equal footing, and if you want your pet to have a flight or a vision Blindly (not currently available) or opposable inches, you must buy it using the usual abilities.To this end, the rule you are talking about is: if you choose an animal that you (or a reasonable person) would like to have one of these animals you must take abilities, which reduces the number of other abilities you can grant.That, in a way, makes some animals inferior to others because you have fewer and fewer options every day for the selection of your familiar abilities and your master., the implementation does not support the intention, assuming my assumption is correct.
Realistically (with the approval of GM, of course), you can state that your owl has a broken wing (or a congenital anomaly, Finding Nemo) that prevents it from flying normally, so that if you do not want to spend a familiar ability, one day to let it fly, it just can not and you're not penalized for choosing a flying creature as a familiar person (since familiar abilities, like says the book's illustration, allow you to place wings on a cat if you wish so that any pet can fly).
In short, taking a pet that naturally has one of its familiar powers is a penalty under the rules, because you are now obliged to spend these points, where it is optional for a normally less talented animal, hence the reason why I propose trampling an animal. As above, the natural abilities of the creature allow you to have your owl for aesthetic reasons, without your selection of abilities being limited.
More to your question, you are right to say that there are no statistics for an owl. There are statistics for a viper and an eagle (even if they are small), but apart from these statistics, the closest statistics you can get are the animals described in the Animal Companion section, but their size is small (or average). great in the case of the horse) and are supposed to be considerably higher than average examples of their kind, so it provides barely more than an extreme upper limit. Here (and in the statistics block for Eagle), a bird has a flying speed of 60, which you can not even know if you master both Flier and Fast Movement (40's) . So it's far from perfect, and "bird" covers a lot of ground – it would be fair to say that owls have a dark vision, unlike hawks, and none of them are nasty. A blind vision, while bats should be.
The best advice I can give, aside from diving into some Pathfinder 1e books or waiting for more second books (or official online resources) to come out, is simply to choose what makes sense and solve it with your GM. . Cats, owls, hawks, snakes (ignoring poison), etc., are quite easy, but a bat, since it does not have the familiar blind ability, is a beast different (pun). Some would argue that blind vision might be too powerful for a familiar ability, others would say it's just the rule at home, and others might suggest not to allow bald ones until official guidelines are available.
At the end of the day, this is a call from GM, but I will not miss it because you still have to pay for the feature. In fact, it is advantageous for the player to say that owls do not have dark vision (or do not fly) and that cats do not go up, so you can choose these abilities if you wish, without to be forced.
The pet rules state that pets can attack using your level as a modifier, but the lack of statistics means that we are alone in determining the amount and type of damage.