There's no way to auto add an inventory item to a quick slot, which is likely good as I think it would frustrate players who usually take great pains to personalize their own slots.
As for being able to increase the number of times a PC can cast a certain spell, we'd need more details as to the -why- of it.
If this is for just your own use when playing in SP mode, you could just make an override of the relevant spells gained 2da(s) and up the number of spells available at each level as desired.
You could also create custom feats for specific spells that you incriment/decriment accordingly based on whatever parameters you decide on.
Lastly, you could create custom rods, wands or widgets that either cast specific spells using available item properties with charges or uses per day, or even create an item that stores spells cast into it and even multiplies the uses when you do so.
Anyhow, more details would be required before options can be narrowed and roughed out for you.