[quote=Saltwater Thief]
Brand/Headphones, quick question- since I suspect there's a limit to my ability to make constructs, what would that limit be based on? Size, number of constructs, distance from me, all of the above...?
[/quote]

Here is my explanation, if we were to accept what Bran has said in the past about "a construct" being equal to "an ally", "a pet" or an "elemental creature" from games:

You are correct in your last presumption. There are many factors that influence the existence of a construct, all of which stem from the user and the surroundings. 

A mage must be completely concentrated when devising the construct, because they must give it a purpose as well as an accurate form, and, even after it has been created, the thought of its existence must not escape the magician, nor must it leave a specific perimeter around them. The length of the area, in which the construct will naturally be bound to, depends on both the order given by the mage and the level of the mage's construct skill. The more they have trained with creating and advancing the construct, the greater the range will be. A mage must also have strong willpower for the construct to exist. If they were to be swayed or fall in spirit, it is very likely that the construct will self-destruct, or, if they were to perchance have a wave of different emotions clash within them, there is also the possibility of the construct going wild and disobeying the given orders. 
Of course, the number and size of the constructs also matter and they are linked to the magi's ability mastery. An experienced one would be able to create bigger and stronger allies, yet an average mage would most likely be able to "summon" either one powerful construct or several (2-5) weaker, but efficient ones. The higher their number, the harder it will be on the mage. Their energy will decrease faster, due to the fact that both they and the construct(s) are using the mage's fuel, not to mention that their mind won't be able to handle the pressure. Creating such an elemental creature causes strain on the mind and the longer it remains in existence, the more the brain is burdened. If it is only one and weak, then it wouldn't be a problem, but anything greater does tire the body out. Naturally, it still depends on how skilled the magician is, but even a master would feel exhaustion after awhile. 

Finally, the surroundings also have a say on the matter, yet I believe there shouldn't be any need for a lengthy explanation here, because it truly is common sense. If the temperature is below zero or too high, a water construct is likely likely to be unstable. If it is raining, a wind construct will be difficult to create and maneuver. That is how it is. In such situations, the constructs greatly rely on the mage's energy supply and willpower.

I would like to note that the mages, who are capable of creating many stable constructs, will likely lack in other magical abilities. Constructs are, after all, an elemental magic with a part of the magician's will within it and not simply a formulated order. They take a long time to learn and stabilize, thus the training in that area will hinder the development in other places. 
Imagine it as how in an MMORPGs we have the "magician" class, which can advance as either a "summoner" or a "wizard". The latter would be a mage with a specialty in constructs.

If I had to speak about Skye, I'll have to edit his hydromancy, because at the time I did not know what constructs exactly were. There is no way he would give something free will XD He's far too controlling.