Okay you want to do this now or the next day when, if Bolin and Asami agree, they approach Lin about getting on board with the investigations?

I was going to bring Korra back there. Depending on if Bolin and Asami agree, she'll want in, and it'll be like the earlier situation never occurred. 

Taking on a bit much as in taking on too many responsibilities for Tenzin at the moment? I'd say yes, revert them back to a more 'prime' age. Mid or late twenties at least. Considering Jinora's eventual character development throughout the series, she's gotten really capable. If you'd want to think about the age increase for the kids or decrease for the TenLin, we can, no rush.