2. I think the answer to this is to use the summoning skill (Essence Companion).
3. Not, caster and summoned creatures are only linked by mental control, not by soul link.
And about point 1, there are no rules about this, but I think you could use some (summoned levels / caster level) ratio if you like. But if you require 'summoning' skill to determine the summoned creature level, I think this is not necessary becuase now it depends on summoner skill instead using directly the level. This rewards to caster that effort in summoning developing the skill, using the level is too generic IMO.