AusBonsai

Just bumping this back to page 1 so an experienced grower can help with cultural care and maintenance.

Most of us would allow these to grow on for a few years to thicken the trunks. Most Eucs respond well to trunk chop so even if they get tall you can cut back confidently and expect lots of new shoots on the stump.
I repot around this time of year when required, removing up to 3/4 of roots.
Feed with any plant fertiliser as Eucs are not really fussy about Phosphorous.

Yes, as a general rule, to get a solid trunk, spend the first few years growing long, and cutting back hard once a year - Eucs are fine with this. Larger and larger pots each year, fertilise heavily, full sun, water well, go crazy. When you have a framework, you can start to refine branches and foliage, and reduce the root ball to fit a bonsai pot. Take your time, and relax. You don't get a thick interesting trunk by keeping a small tree in a small pot!

Eucs will usually grow quite quickly, so you will need to get the wire off within a couple of months - watch carefully!

Gavin

As for species, they might be Eucalyptus melliodora (Yellow Box), but you'd need to ask the folk who sold them to you.

G