I have the 13.5 EVO too. I think 3-4 little fish is about the max you'll want to do on this. A single occelaris is a good move (I have a pair of orange storms and a tailspot blenny on the way - that'll be "full" for me). A pair of clowns can get territorial and make it tough if/when you add a new fish. A single clown is a much better tankmate. I'd go with the following based on your criteria:
- Single occelaris
- Tailspot blenny
- Possum wrasse
- Yellow clown goby
I'm a big fan of the tailspot blenny. It's not much for color (though not ugly), but it's an incredible personality. My previous one (I had an ich outbreak in my EVO and went fallow until earlier this month) essentially "paired" with my single davinci clown. They'd spend the day side by side in my GSP and at night slept together next to the overflow in the rear of the tank. The blenny would even herd the clown into the GSP if it was too far. They'll also watch you like an angry old man watches kids getting too close to his lawn.
A possum wrasse is an excellent tankmate in one of these. Peaceful, pretty, active in and out of the rockwork, and a nice compliment to the relatively stationary clowns and the bottom/rock dwelling blenny. Not many free-swimming options for this system.
The clown goby is cute, small, bright, and peaceful. It's often lost in a larger tank, but very visible in the EVO. It shouldn't have issues with the blenny assuming you have enough hiding places in the rockwork. I'd have one in my tank, but they nip at acros and I've worked really hard to get my acros growing in this tank.
Honorable mentions: Orchid dottyback - beautiful purple color and fairly active once settled. The downside is that they can be territorial and aggressive toward similarly sized/shape fish (like the blenny). Pink Streak Wrasse - Fine fish, impossible to find. Any shrimp goby (especially paired with shrimp) - very neat fish, but prone to jumping (through spaces you can't even imagine they'd fit) and yet another bottom/cave dwelling option.
I'd pass on the dragonet unless you are able to buy live pods to supplement and feed regularly. I also think the midas is a bit too big for this tank - I'd go with a tailspot or flametail instead.
