There is no defined order of effects, no.
This is generally taken to mean that the controller of the effects may choose to use them in whichever order is most beneficial to him or her. I’m about 95% sure that 3.5 codified that somewhere, but I don’t think it was in core so I don’t know if Pathfinder ever wrote that down anywhere.
Still, in the absence of a defined order, it makes the most sense for the person who has the abilities to control the order.
Most creatures are summoned unwillingly, or are otherwise unhappy about being summoned.
The Monster Manual is rife with examples of creatures that hate being summoned, under almost any circumstances. For example:
Devils: MM (67):
However it is summoned, a devil brought to the Material Plane typically resents being pressed into service. However, the devil seizes every opportunity to corrupt its summoner so that the summoner's soul ends up in the Nine Hells. Only imps are truly content to be summoned, and they easily commit to serving a summoner as a familiar, but they still do their utmost to corrupt those who summon them.
Yugoloths (a specific circumstance) (MM 311):
A yugoloth summoned using its true name, as inscribed in the Books of Keeping, is forced to serve its summoner obediently. The yugoloth hates being controlled in this manner and isn't shy about making its displeasure known.
Elementals (MM 123):
Certain spells and magic items can conjure an elemental, summoning it from the Inner Planes to the Material Plane. Elementals instinctively resent being pulled from their native planes and bound into service. A creature that summons an elemental must assert force of will to control it.
Demons (MM 53):
A mortal who learns a demon's true name can use powerful summoning magic to call the demon from the Abyss and exercise some measure of control over it. However, most demons brought to the Material Plane in this manner do everything in their power to wreak havoc or sow discord and strife.
(MM 51):
If a single mistake is made, a demon that breaks free shows no mercy as it makes its summoner the first victim of its wrath.
One exception is a Glabrezu (MM 53):
A glabrezu takes great pleasure in destroying mortals through temptation, and these creatures are among the few demons to offer their service to creatures foolish enough to summon them.
The Gate spell is explicit about simply pulling any creature away without notice:
When you cast this spell, you can speak the name of a specific creature (a pseudonym, title, or nickname doesn't work). If that creature is on a plane other than the one you are on, the portal opens in the named creature's immediate vicinity and draws the creature through it to the nearest unoccupied space on your side of the portal. You gain no Special power over the creature, and it is free to act as the DM deems appropriate. It might leave, Attack you, or help you.
The Conjure Fey spell implies that the fey resents being summoned, since it attacks you if you lose concentration (much like a demon):
If your Concentration is broken, the fey creature doesn't disappear. Instead, you lose control of the fey creature, it becomes hostile toward you and your companions, and it might Attack.
Confusingly, the Conjure Woodland Beings spell does not have that clause. Indeed, you could summon the same creature with either spell, and it will only attack you when you lose concentration only if you used the higher level version.
The only case that might allow for some free will is Conjure Celestial, because it has the freedom to only obey commands that follow its alignment.
It obeys any verbal commands that you issue to it (no action required by you), as long as they don't violate its alignment.
Best Answer
There is no limit, yes, and yes.
But you the Cleric cannot choose what will come. Per the text of Planar ally:
There is no limitation to the creature's CR of any kind. The DM will most probably try to make it fit the scenario and fit your relationship with the otherwordly entity. Note though that the summoned creature...
...although it is sent to primarily aid you:
Still, you should pray to your DM right after your Cleric finishes praying for a planar ally.