Unironically build whoever you think is fun and useful overall. Healing Defenders and Jaye are handy to build.
Arene, Beanstalk, Bubble, Jaye, Cutter, and Utage are fine e2 candidates and cheap. Podenco's a good one too.
For your 5 stars, there's a few fun options.
Bena's a unique unit and pretty decent. She's guaranteed to survive any one hit. Tequila's just a sorta mini-silverash in terms of damage. Shamare's the best debuffer/buffer in the game that isn't limited. Whisperain, April, Blitz, Broca, Manticore, Robin/Frost, Bibeak, Glaucus, Scene, Kafka, Beeswax, Mint, Asbestos, Heavyrain, Pramanix, Astesia, Zima, Absinthe, Warfarin, Silence, Liskarm, Reed, Blue Poison, Platinum, Leonhardt, and Nearl are all good 5 stars to e2. I'd say prioritize who you *want* to be using that gets the biggest bump from e2.