1. Only lowers prices, so only worth if you know you will contact him frequently.
Not entirely correct. If you raise an NPC's attitude above 50 they will fight as your allies if you start a combat in their surroundings.
In addition to that, their friends in the surrounding area will also join the fight. These friends won't count as your allies but they count as neutral NPCs that won't hurt you in combat but will fight against your enemies.
This is really cool if you are doing a solo playthrough, or if you want to fight some enemies that are too strong for you. Just "bribe" some NPCs and they will help you take down the enemy.
It's the main reason why I raise their attitude. The price reduction is an added bonus.
I haven't tried raising an NPC's attitude to 100, so maybe there will be a benefit to that as well.
Regarding Telekinesis: You can move anything regardless of its weight. The Telekinesis stat only affects the range.