FYI, the total number of followers your charisma can support can only be 5. You can, again, only have 5 followers since charisma do not go over 20 unless you cheat. Even with backgrounds, you cannot increase Charisma to more than 20.
Next, when I meant they "do not count", I mean that they do not take follower slot. Dog do not take the follower slot. See for yourself. Also, there are other followers that do not take follower slot including Arronax and Bane of Kree. Which concludes that you haven't finish the game yet.
Now, when I meant Persuasion (expert), it means that you will gain +1 bonus in your number of followers if you have persuasion skill level 3 and is an expert in that field. Read the manual or visit my site for more info about persuasion.
Yes, I do agree with you that you cannot take your summoned creature for a very long time since they will disappear if you sleep or if you loose all your manas. However, your familiar can be with your team and not take up follower slot for as long as you want. Cancel that, he will never go away unless he got killed or if you use Disperse Magick.
Back to summons. Yes, they can not exchange inventories with you but they do stay with you during battles and thus they are followers. You can control up to 5 followers as per intelligence.
My original statement was that you can have up to 15 followers and then someone (at the other board) made some corrections and said you can have up to 20+ followers. I don't know the exact number but that is what he said. He did list all of them.
What else would you like to know?