Anything? Here's something; The 45 gal
tank you now have and the 57 you like seem to have the same dimensions, must be some sort of tardis tank.
I don't see much to be gained in only going up only 12 gallons, moving up depends on if you want more length, height, or front to back depth. Your 36" light can easily handle a 48' long tank, only 6' longer at each end,probably a 60". Depends on height of tank and depth of water, I wouldn't go much deeper than now if length gets much more than 60. It'd be nice if you could move the light from end to end , front to back, from time to time to ensure more even lighting.
Just get tank from reputable maker and dealer. Rimmed or not? Just personal preference but I don't like seeing water surface and air above it in tank, so I like a wide top rim, less chance of filling too close to top and slop over. You may have plants that grow out of water, so thin rim or rimless may be your choice. Rimmed is easier to set a sectional glass top in.
This is strictly plants? No fish? I've had some really heavily planted tanks, never used C02 augmentation, but tanks were heavily stocked with fish.
That's all the anything I got.