
Addressing 3 with a side order of 4 at the end:
I actually think summoner is a little easier than dragoon...
Dragoon - in the sense of job crystal dragoon - is very Ishgard-exclusive. Only a character who was born there or raised there for a significant portion of their life would really be able to access this job. They likely would have been on the frontlines against the Dravanian horde for a long time before they earned the right to train as a Dragoon - losing many many comrades in the process. They would have been put through rigorous, re-traumatising training. And then something must have happened to cause them to stop being in active service. And then the war they gave up their personal life to fight is ended and they're just meant to make peace with the dragons?
Basically, it's a very specific character archetype: bitter, Fury-fearing war veteran.
Summoners, on the other hand... while they still have certain set things that have to have happened in order for the character to be capable of becoming a summoner (have been present at the defeat of a Primal; have a certain level of aetheric surplus and basic magical talent; have access to a soul crystal), it doesn't place any limitations on where the character can be from, what type of personality they have, what their family history is like... They'll probably have at least one trauma in their backstory (how did they end up fighting a Primal?), but beyond that? There's much more freedom, and much more range as to "this is what a summoner looks like" in roleplay without people having to set aside the lore in order to suspend disbelief.
To recap, here are the things you need to consider when making a summoner character:
• They absolutely must have been present at the defeat of Ifrit, Titan, and/or Garuda, and they will only be able to summon egis of the primals they have been present at the defeat of. (So if they were present at Garuda's defeat, they'd be able to summon Garuda-egi but not Ifrit-egi or Titan-egi.) This is non-negotiable. No Primal defeat witnessed = no egis. There's a few ways your character could end up in such a situation - some consensual, some not so much - so there's still options here.
• They probably need a background in magic. Arcanima is the standard route - this is taught by the Arcanists' Guild in Limsa Lominsa, who seek to spread the art of arcanima so that it isn't lost over the generations. But I could see justifications for a conjurer or thaumaturge seeking tutelage in Summoning as well.
• They need access to a soul crystal. In the SMN's case, these are ancient Allagan artefacts, and so far most of them seem to have been recovered from the dig overseen by the Sons of Saint Coinach in Mor Dhona, near the Crystal Tower. Either the character should have scholarly ties to the Sons, or they should have motivation and ability to try and steal a crystal from this dig.
If this is still too restricting, or doesn't click with you - there's absolutely nothing wrong with making your character a regular old Arcanist (or Lancer, for that matter). Arcanists can still summon Carbuncle through the use of arcane geometries - there's a game feature now where you can make your in-game "egis" look like Carbuncle, too, so you don't even have to worry about what to do if you want to run duties IC. And they can still reach excellent levels of power, so please don't worry about always being "weaker than" any other characters who happen to have job crystals.
In fact, most RP characters I've met in this game don't have a job crystal - they're just a regular person, who happens to be trained in certain magic disciplines, or capable of using certain weapons. (Or sometimes neither. There are pure Disciples of the Hand/Land I've seen, too.)
I actually think summoner is a little easier than dragoon...
Dragoon - in the sense of job crystal dragoon - is very Ishgard-exclusive. Only a character who was born there or raised there for a significant portion of their life would really be able to access this job. They likely would have been on the frontlines against the Dravanian horde for a long time before they earned the right to train as a Dragoon - losing many many comrades in the process. They would have been put through rigorous, re-traumatising training. And then something must have happened to cause them to stop being in active service. And then the war they gave up their personal life to fight is ended and they're just meant to make peace with the dragons?
Basically, it's a very specific character archetype: bitter, Fury-fearing war veteran.
Summoners, on the other hand... while they still have certain set things that have to have happened in order for the character to be capable of becoming a summoner (have been present at the defeat of a Primal; have a certain level of aetheric surplus and basic magical talent; have access to a soul crystal), it doesn't place any limitations on where the character can be from, what type of personality they have, what their family history is like... They'll probably have at least one trauma in their backstory (how did they end up fighting a Primal?), but beyond that? There's much more freedom, and much more range as to "this is what a summoner looks like" in roleplay without people having to set aside the lore in order to suspend disbelief.
To recap, here are the things you need to consider when making a summoner character:
• They absolutely must have been present at the defeat of Ifrit, Titan, and/or Garuda, and they will only be able to summon egis of the primals they have been present at the defeat of. (So if they were present at Garuda's defeat, they'd be able to summon Garuda-egi but not Ifrit-egi or Titan-egi.) This is non-negotiable. No Primal defeat witnessed = no egis. There's a few ways your character could end up in such a situation - some consensual, some not so much - so there's still options here.
• They probably need a background in magic. Arcanima is the standard route - this is taught by the Arcanists' Guild in Limsa Lominsa, who seek to spread the art of arcanima so that it isn't lost over the generations. But I could see justifications for a conjurer or thaumaturge seeking tutelage in Summoning as well.
• They need access to a soul crystal. In the SMN's case, these are ancient Allagan artefacts, and so far most of them seem to have been recovered from the dig overseen by the Sons of Saint Coinach in Mor Dhona, near the Crystal Tower. Either the character should have scholarly ties to the Sons, or they should have motivation and ability to try and steal a crystal from this dig.
If this is still too restricting, or doesn't click with you - there's absolutely nothing wrong with making your character a regular old Arcanist (or Lancer, for that matter). Arcanists can still summon Carbuncle through the use of arcane geometries - there's a game feature now where you can make your in-game "egis" look like Carbuncle, too, so you don't even have to worry about what to do if you want to run duties IC. And they can still reach excellent levels of power, so please don't worry about always being "weaker than" any other characters who happen to have job crystals.
In fact, most RP characters I've met in this game don't have a job crystal - they're just a regular person, who happens to be trained in certain magic disciplines, or capable of using certain weapons. (Or sometimes neither. There are pure Disciples of the Hand/Land I've seen, too.)