Hi Jodie
TBH for a first attempt at keeping dwarf puffers, I'd possibly recommend a regular tank and keep the biorb for sparkling gourami (my 60L biorb started life as a dwarf gourami tank with honey gourami and sparklers in and it was a delightful tank).
The reason I say this is because the standard firltration for the biorb will not be enough for the water quality to be maintained for the cofort and well being of the puffers. I have 4 DPs in my 60L biorb but I have heavily modified it and it runs with sand and a big internal filter instead of the stock filtration. I also have a fair bit of experience in puffer keeping.
They are delightful fish if kept in immaculate, over filtered water, but I think a standard biorb would be more suited to the gouramis really.
DPs are species only tank fish and not adviseable to go in community tanks. They won't care what size a fish is and will take chunks out of them to 'taste' them and see if they are edible.
I have 2 otocinclus in my tank and that is the only fish I would ever consider putting in with DPs.
They eat meaty foods such as bloodworms and snails etc and are FRESHWATER fish. Because they poo for medals and eaty meaty foods they need heavily filtered tanks and weekly 50% water changes to keep the water perfectly clean.
They get feisty as they get older and reach sexual maturity and getting the right mix of males to females and a tank stuffed with plants and caves is essential to break up the line of sight and reduce aggression. They are impossible to sex when babies too.
You couldn't have a sucking loach in with DPs as they will try and eat it.
Hope that helps.
