Grand wood
I’d leave the soil for a bit
Practise some layouts first ... they’re easy to change until you dump in the soil and then everything starts mixing
If you place the lava rock (slightly loose) in some tights/nylons, it’s easy to change things about - the looseness lets you mold/shape the lava “bench”
Once you’ve got a scape you like, let it sit a couple days, look at it in different lights and various angles (& moods)
The disadvantage of a bigger tank is if you decide you’re not really that keen on the scape in a few weeks/months, it’s a major job changing it - another reason to take your time with just growing in the plants, no livestock to worry about during partial rescapes
Depending how much scaping you’ve done or how particular you might be, fill with water at the wood/stone/NO soil stage - underwater and lighting can dramatically alter perceptions
Mark Evans journals are excellent examples of playing with scapes “in tank” ... and then settling on some very different paths