There's some debate about bettas in Edge tanks. It can be done; keeping the water line lower can help. When the water is raised, some betta find the opening fine, others freak out and can't. It'll largely depend on your particular betta but leaving the water line lower can probably help that issue a lot. Otherwise that size tank is a bit limiting (like most small tanks). Most tetras, danios and rasboras (including neon tetra) are very active fish so would appreciate more horizontal swim space. You could do an all shrimp tank, or some nano fish like ember tetra, chili rasbora or celestial pearl danio (you could do the nano fish with the shrimp too; they might eat the baby shrimp but should leave the adults alone).