Planted tanks do not have to be intimidating. You should start off with a low light tank.
I have been making a list of what is appropriate for this kind of tank. Here is a list of the common and species names.
Wisteria-
Hygrophila difformis
Purple Cabomba
-Cabomba pulcherrima sp. Red
Java Fern -
Microsorum pteropus
Windelov Java Fern, Windelov Fern -
Microsorum pteropus 'Windelov'
Narrow Leaf Java Fern -
Microsorum pteropus v. 'narrow leaf'
Java Moss -
Vesicularia dubyana
Green Hygro -
Hygrophila polysperma
Sunset Hygro -
Hygrophila polysperma 'Rosanervig'
Ceylon Hygro -
Hygrophila polysperma 'Ceylon'
Rotala Rotundifolia -
Rotala rotundifolia
Rotala Rotundifolia sp. Green -
Rotala rotundifolia sp. 'Green'
Rotala Indica -
Rotala indica
Hornwort -
Ceratophylum demersum
Moneywort, Water Hyssop -
Bocapa monnieri
Brazilian Pennywort, Pennywort -
Hydrocotyle leucocephala
Crypt Wendtii -
Cryptocoryne wendtii
Crypt Balansae -
Cryptocoryne Balansae
Pygmy Crypt -
Cryptocoryne pygmaea
Guppy Grass -
Najas guadalupensis
Anubias barteri -
Anubias barteri v. barteri
Anubias barteri 'marble' -
Anubias barteri 'marble'
Anubias barteri v. 'glabra' -
Anubias barteri v. 'glabra'
Anubias nana -
Anubias barteri v. 'nana'
Coffee leaf anubias -
Anubias barteri v. 'coffeefolia'
Crypt retrospiralis -
Cryptocoryne retrospiralis
Crypt spiralis -
Cryptocoryne spiralis
Golden nana -
Anubias barteri v. 'nana golden'
Narrow leaf nana -
Anubias barteri v. 'nana narrow leaf'
Petite nana -
Anubias barteri v. nana 'petite'
Philippine Java Fern -
Microsorum pteropus 'Philippine'
Red Java fern -
Microsorum pteropus "red"
Crypt Becketii -
Cryptcoryne becketii
Pelia -
Monosolenium tenerum
Waterwheel Plant -
Aldrovanda vesiculosa
Bacopa -
Bacopa caroliniana
African Water Fern -
Bolbitis heudelotii
Hornwort -
Ceratophyllum submersum
Crypt Aponogetifolia -
Cryptocoryne aponogetifolia
Micro Crypt -
Cryptocoryne petchii
Tropica Sword -
Echinodorus parviflorus 'Tropica'
Downoi -
Pogostemon helferi
Red Tiger Lotus
-Nymphaea zenkeri
Four Leaf Clover
-Marsilea quadrifolia
This is not a complete list of course. But these are plants that I have experience keeping and feel do well in low light. You can find the plant care sheets and other info on this site.
PlantGeek.net - Plant Guide
or this one
AquariumPlants.com Largest online sales / service site for the live aquarium plants & aquarium products community.
The advantage to a live planted tank is that live plants use nitrates and oxygenate your water further. They also add another dimension to your tank that fake plants just can't. It is really up to you though. You can also uyse fake plants, just get alot of them. For me, I would much rather spend money on real plants taht can grown and fill in space than fake ones. Just a preference though.
Also, this is just a thought. Puffers require a high protein diet and eat live or frozen fresh diet,...without other community fish to eat the remains of what you put in, the owness will be on you to clean out what they don't eat and keep the ammonia and nitrates under control with the excess food. Be diligent on water changes and getting out the excess food.
Grats on the free tank. It isn't the best choice for keeping puffers. Perhaps you will eventually get a longer tank and can use the hex for fish who prefer height.