Welcome to Fishlore.
The simple answer to your nitrite/nitrate problem is: 'Too many, too early'.
Don't worry, we've all done it
Your pH seems very high, I would be aiming to get it back down to around 7.4, but you need to do it gradually. Remember pH is not linear, so bring it down gradually. Your plants will appreciate it as well as the fish.
Keep up the water changes to remove the excess NitrItes and NitrAtes until your filter catches up with bacteria.
Regarding your filtration, you can definitely get an appropriate Canister, and I would recommend one. You want to aim for a filter that will turn-over your water at least 4 times an hour, you have 37G (170L), so look at 150G (680L) /hr or higher, especially with your population.
Depending on budget, I would personally go Eheim, the Classic 2215 does 620L/hr, the Professional 2224 will do 700L/hr. You could also look at Fluval for a cheaper, but still decent, the 205 is rated at 680L/hr.
If the flow is too strong for your community, you can reduce the flow rate on Eheims by drilling the holes in the Spraybar wider, Fluval's have a valve that can be controlled.
I run an Eheim 2213 on my 70L and a Fluval 105 on my 25L.
Remember: If you do put a canister on, you'll need to let it cycle up before completely removing the old filter.
HTH