I generally play a more supportive role on a chibi while using weapons to counter bots at a defensive stance, Wide Beam Gun, Handy Zook or Burner (Glass Burner > Burner, but Burner is 3s from uc garapon right now) are usually my first choices and can all be gotten 3s. Peacekeeper is also a pretty good gun. Unless the chibi can get Broad Radar or something awesome like that, I tend to shy away from going to level 10. When I tune I (of course) try to get my str and tec even and high, and pick a movement stat to tune up a little bit, usually always walk. I also tend to get sway if I go to level 10, though I dunno if it's a great idea in reality, rofl.
One thing to keep in mind is that no matter what chibi you are, you were never built to be offensively superior, you can strive for it but someone will always do it better then you. Trying to get a good DPS is alright, but keep in mind that every time you run to the front lines and die, you have no one to blame but yourself and no amount of help will make you better then non-chibi bots. They were built with a heavy emphasis on supporting, not fighting. Also, Melfi-chan and R.Winberrl-chan are both better healers, and while their circle/abilities are generally considered better, they still can never give long range and ammo refill if they wanted to. I'm just pointing this out so you don't feel like you're being all too restricted with UC chibis; the RT chibis are just as helpless in battle situations with just different circles or different ways to support.