Took on the summoning biju portion, which mostly could just use word breakdowns:
Summoning Tattoo: The Summoner will be sealed with a tattoo. Using the tattoo they summon the bijū for use. This Tattoo counts as a bijū chakra signature so hunters can find them in the same way they would a real host. Just don't metagame when you are doing an IC hunt.
Chakra Cost: Bijū cost 20% of the user's total (not current) chakra to summon, even one after the other.
Controlling Mechanism: Bijū must be under the influence of genjutsu at all times while used as a summon. This uses 5% of the summoner's total (not current) chakra while it's being used as a summon, the drain stops when the bijū has been removed from the field. Paying for the cost of summoning the beast using the chakra of the beast is not allowed. Mastery of the beast is not possible because a summons Bijū is hostile to its user.
Severing the Summoner's Control: The control of the summoner over the Bijū can be broken by: The manga/anime use of the Contract Seal Jutsu used by Minato in his fight with Obito the night of the nine-tails attack or dispelling the genjutsu [cost is 20% of your chakra]. For Rinnegan users, the chakra rods have to be removed from the biju and you have to then break the the genjutsu that controls the beast. Success results in a rogue Bijū situation that will need to be subdued.
Restrictions: Summoners can only do one action per turn as long as the biju is summoned. The action can be for defense or for attack.
Just strike the biju enhancement/encasement thing altogether. If it's not prohibited it doesn't need to be mentioned at all under restrictions.
Drawbacks:Summoned Bijū will always have a hateful feeling towards their summoner. Should a Bijū ever get the chance the ability to act on their own, they will target the summoner first, no matter what.
Death of Summoner: If the summoner dies, and the Bijū has not been summoned, the challenger/hunter will transfer the summoning tattoo to themselves and win the beast. However, if the summoner dies while the bijū is summoned, the Bijū goes rogue. Then the challenger/hunter can attempt to subdue and capture it , if the beast has not already been captured. The rogue bijū will be GM'd by the defeated summoner. <--- Under discussion.
Now, if the summoner is also a host, and dies, the hosted bijū will come back to life and appear in 7 days at the location of the host's demise: the biju council will decide who GM's the biju then.