Upsizing from nano to 20gal long ... but how exactly?

[MotorcycleBoy]

I got my gear (much of it from AC-O, thanks!) and I'm (finally) upsizing from my nano (2.5gal) to a 20-long!
So, how should I do this, exactly? (Doh! Noob) 
I have one betta and 2 snails currently, and some plants. I plan to keep the nano as a quarantine tank. (I'll be adding to the collection in the 20 with a few betta-friendlies and more snails.)
Do I...
A) Take some (maybe half) of the substrate and maybe 1/2 the plants to the new tank along with half (~1gal) the water; then fill up the tank most of the way and treat it like I normally would (Stability, etc.) for several (6-8-12?) weeks until it consistently tests as cycled? (Then move the creatures over to the new tank, along with the rest of the stuff.)  
B) Move everything over and add 2 gallons of water (essentially, like a 50% water change) creating 4 total (shallow and long, but I don't think they'll mind that? It'd be ~20% full then); treat as usual, wait a week, test, add 4 gallons (total now 😎 like another 50% water change; repeat, adding 8 gal the next time (now at ~16), then one more time to add the last bit, then continue regular maintenance?  
C) Neither; something else?

Also, what's easier to maintain for the quarantine tank: completely empty other than water (cycled, obviously, and continuing to monitor it) or keep some substrate and even a plant or two in there? Maybe even one or two snails? When it's not in use, how should I maintain it in readiness?

TIA; never done this before. 🙂 Only a little over a year into this hobby and only with the one fish. 

[binkysmom]

what filter are you running? I would just move the filter over to the new tank and start with fresh water. If you want to move the substrate and plants/decorations over you can.

I just run an extra sponge filter in a main tank and move it to the quarantine when i get new fish. I keep that one tank empty and bring it out when i need it. it's ugly so i'm not super tempted to keep it as a display. It only has water in it when i put fish in.

Irene from Girl Talks Fish has a good video on quarantine tanks. She uses a plastic (Rubbermaid?) tote.

[MotorcycleBoy]

The filter is one that is designed for the nano tank. I've supplemented it with sponge on the intake and sponge on the outlet to dampen the water movement primarily, but I'm sure it has picked up BB as well. 

I have a new HOB filter for the larger tank. I'm also using a small airstone with a small filter for it just as a supplement. 

I want to move the plants over so they can grow and expand better, and will add to them, of course. 

Good idea. So, when I need the Q tank, I could just move the sponge filter over. 

Thanks! Just don't want to crash it, cause major stress, or otherwise mess up in a way that kills the critters.