Tena
If you've decided not to do a guided trip, Tena is definitely the place you'll want to base out of. There are tons of restaurants, hotels, and opportunities to rent boats and hook up with other kayakers.
There are numerous cheap hotels and restaurants in Tena, as well as taxi drivers that can help you out with shuttle. If you'll be staying for a month or longer, consider renting a house to save more money that way.
The Welcome Break has historically been the "kayaker's hang out." Favorite restaurants include: Chuquitos, Marques, Pollo Sin Rival, and the Pizzaria Hilton.