Agree with Trips on the starter lifesteal gear. This should essentially be the main gear that Kael will use for a long time, including Dragon, Campaign Brutal, arena and CB. It should be the 4 star lifesteal set, and the boots should have speed as their primary stat
While you are building food to get additional champions to 60, you can start to build out teams for other areas. Arena for example can have a well built team where most aren't 60.
For Apoc, make sure you throw as much speed on him as possible. This includes speed sets, plus any gear that has speed multiplied when you upgrade it. Anytime you get another gear with speed check to see if it is better than what he has before giving it to others. Ideally he is going to be the fastest member of your team.
Farm a spirit host from the dark elves campaign stage and keep her to level 30, but you will need to ascend her to level 3. For arena, put her as your lead for the 10% speed aura, then have Apo, Tayrel and Kael in. You will want the speeds of each champion to go in the following sequence: Apo (turn meter boost and increase speed), Spirit Host (increase attack), Tayrel (decrease defense) and then Kael (AoE attack). Kael is the only one that needs to be 60 for this to team to work, and you can start to farm medals and get through some missions. It should be able to comfortably take you up to mid silver.