I would take the design step by step, especially as you are omitting some details that will radically effect your set-up. I am also taking into account that you would like the 'cleanest' / minimalistic look.
- Decide on the tank first: 12Long and 60-P are 2 very different beasts, with 12L being the hardest of the 2 to set-up and run.
- Consider the location of the tank: will it be on a stand with the utility space underneath and against the wall or will it be on a desk or a bar counter (like mine) visible from all sides? If it will be on a traditional stand, you have a lot more options with the equipment.
If the tank is in the 'open': all of the equipment will be on display and that would rule out in-line heater (like Hydor), traditional co2 set-up, most of the canister filters, spray bar, glass pipes, and so on.
the 12L will be your first challenge.
- If the tank will be mostly planted with carpeting plants, you might be able to get away with a single canister filter.
- If the tank will be heavily planted with taller plants, you will end up with 2 filters, one on each end of the tank.
In either case, VIOLET GLASS JET (OUTFLOW) JP-1 13D (or similar) is what you will end up with. Consider that the outside bottoms of 'glass pipes' will come to ~2" of the surface the tank is on. Unless you can drill holes in the surface to connect them to the filter(s) underneath, your filter hoses would be visible.
If the tank will be on a traditional stand, then Eheim classic filter(s) are hard to beat. If the tank will be in the open, 2 x Finnex FX-360 (or similar) is pretty much your only choice of canister filters.
: will it have to sit on top of the tank or can you hang it? That will affected the options you have. Then consider the plants you want. More color = more light = more headaches. Another consideration is how you personally will be 'viewing' the tank. Shallow tanks are designed to be viewed from the top. That's one of the reasons why you pay extra for the rimless design. If that's the case for you, then you either have to hang the light or get a light fixture with adjustable legs. That narrows your options even more. For example: high light + suspended would rule out Finnex Ray 2 for me: a) not enough light b) you have to DYI the way to suspend it. If you mount Finnex on top of the tank, you will have to move it back and forth every time you want your hand in the tank. If you decide to get it anyways, do get the DS model.
I personally ended up with Hagen Glo 2xt5ho mounted on the tank. The Glo has height adjustable mounts that solve the issues above.
if you have no other choice but to go with a 'mini' system, consider Fluval 88 - it works, it's reasonable, customer service is great ime, but most importantly, the refills are readily available. What if ADA's ship is stuck at sea? Your plants are dead. Otherwise, pay the price and go with 5# or 10# tank and get the usual regulator/solenoid/valve set up. You will end up there anyways, sooner or later.
: again, decide what 'look' do you want first. If you want forest/jungle/top-to-bottom/dutch look, there are tons of plants to chose from. Even though the tank is so shallow, there are still stems and swords you can use.
Enjoy the journey.