Aquariums: Moving fish to new aquarium; does my plan seem okay?

So! My fish have been in their 15g standard aquarium for about a year and a half. Im planning on moving them to my new 12g Long tank so they have extra room to swim unobstructed length wise. I also have a bigger canister filter on the new tank, as well as better light, aqua soil, etc etc. The new tank will have new substrate and decor, but iv had it running for a little over 2 weeks to let it marinate a bit and develop a little funk to get things going. My plan is to move over all of my fish and most of my established plants into the new tank, put the old sponge filter into the canister filter and leave it there that way it is available if i ever need it for a hospital tank. I also plan on bagging some of the substrate and putting it into the canister as well (eco complete so just crushed lava rocks) so there will be as much beneficial bacteria as possible going over. Also going to keep as much of the old tank water as i can. I think the water volume between the two tanks won’t be too different since the new tank has thinner wood and a big canister filter that holds a little over a gallon. I just love the long profile and want to give my fish the extra space they need. Ideally i should have bought the 16g long, but got a great deal on the 12g. Does my plan seem like it’d work? Aqadvisor has me at 90% stocking with 1x small female apisto, 8x ember tetras, 10x green neons, 5x false julii, and a sparkling gourami that i’m taking over from my friend who can’t keep him anymore. The new tank will be pretty tannin heavy as well, just hoping the suckers can adjust from the 7.4ph to the new 6.8ph that the aquasoil brings it down to. Thanks guys.