What percentage of my mgmt fee and carry should I give a new partner if I'm already a year into the fund?

It's not uncommon to see 10 - 20% of the carry with vesting and a cliff for an additional partner at this stage. Sometimes more. Use the guidlines of the Venture Share agreement: https://govclab.com/venture-share-2/

However, don't put anything in writing. Once you come to terms verbally, then ask your Decile Partners team to help you get the agreements setup, check and update your cap-table and manage the process.