http://www.d20pfsrd.com/feats/general-feats/leadership---final
You can get what is on the table.
So if your Leadership score is 17, you have a maximum of 30 level 1, plus 3 level 2, plus 1 level 3, plus 1 level 4 followers.
Your DM is saying they don't just show up, you have to recruit, so you could have fewer followers at any given time.
Since you mention you have a "base of operations" you could have followers guarding/caring for your base. Perhaps you can have them do research, run a business, or other things that the DM permits.
Spellcasting followers might make magic items (such as minor potions or scrolls) as well.
Really, Leadership is very hard to help with on the forum, because its basically all in the DM's hands what followers (and even your cohort) will or won't do, what they are or are not capable of.
Since you are a cavalier, with a squire, I imagine your character is a sort of knight. If so, maybe your followers are horse-trainers, smiths, a castellan, and other jobs that support your role.
If your character was a witch or druid, they could be members of your druidic circle or coven.
It really is wide open for you and your DM to discuss and implement how it best suits your game.
The main draw for Leadership is that you get a Cohort, who's generally 2 levels behind you (I recommend a Wizard if you do, you can never have too many buffs!)
Followers are best used as information sources and generic soldiers
Nobody take a small army to the tomb of Dwarfeh the dwarf king, where every hallway is 5x5 and the entire floor f the tomb is a trap
You may take them there to be your deal up crew, BUT some will die
My plan with my cavalier was to have the higher level follows be my camp followers when I'm adventuring and having my cohort run my diplomatic missions and such( since our dm has ruled them out of combat)
The rest would be griffon-riders in training
Probably cavaliers sitting back at my fortified manor until I need them
I brought my Cohort with me into battle and he was generally very fine. Ring of invisibility for sure on him though, 2 hit dice behind on d6s and you don't want him in the line of fire! Spellcasters work great as cohorts because you can invis them and just have them cast buffs all combat + occasionally throw out some high level debuffs. (My cohort's two most popular spells was Haste and Phantasmal Web, where the latter frequently wrecked multi enemy encounters).
My gm has ruled that cohorts can cat hour per level or above spells , but other than that nothing else
No crafting slaves either
There's seven of use, so we don't need cohorts anyways, but my cavalier (who is of highly noble blood) needs a squire and a diplomat for when he's busy adventuring
BTW
Followers can make great after combat healers if your willing to retreat to the entrance of wherever you are, and have them there waiting for just that purpose
And it's even better if your mythic and taking the divine source path ability
So they are all clerics that worship YOU