If you are a woman (+- 60kg) I think 9 and 14 would be the best combo. The wind goes up to 25kn on the best days so you might be a little overpowered on a 9 but still fun and the 14m will get you going in the LW days which are pretty common here. If you plan to go kiting in other spots you might need a 7 tho. You wont need many clothes in Rio anyway, so try to stick the 7 in too
If you are a guy (+-80kg), the 12 should be your main kite in Rio. The 14 wouldn`t be so much of a lightwind kite and I would bring the 9m, specially if you want to kite in other (windier) places.
In Rio I dont know of any kite rentals, as its not a kite destination. Most of the windy places rent kites for approx R$ 60-150 or 20-50 Euros a Day (Kite and bar only), depending on the place and the gear you want. If you can find a rental in Rio, I bet it will be on the expensive end.
Keep in mind that in Rio the wind is not so consistent, and even in the good season, you can expect decent conditions on 2 or 3 days a week, 5 days on a really good week, and usually after 3pm. If you can, I highly encourage you to visit other places, wich are cheaper and offer perfect wind, waves and flat water.
Hope to see you guys soon in Rio!