After reading some advice on that topic i decided to rather get my H. maculata in there.
I've kept the original soil that came with the Bonzai. I'm thinking maybe i should change that...
I've also kept the original base of the plant too, just had to trim it to fit.
I also cut holes out of the base piece glue to allow for water drainage.

I like the idea! Just think it would work better in a bigger enclosure.
Like in a 20x20x30 to give the tree a bit of room cause it is gonna grow
and in that way it will be easier to maintain.

Hey Spinnerhead, that looks great!

There is just one or two things that you would need to look out for. Acacia prefer full sun or at least morning sun. If you keep them indoors you'll have to look for common greenhouse pests.

You'll have to allow the surface of the soil to dry between waterings, which can have an effect on the humidity for the H maculata,... although I suppose a waterbowl could also work.

That is the only things I can think of that might be a problem.

Do Bonzai's have the same light requirements as their fullgrown originals though, what with them being meant to be indoors Frooti?

A bonzai is just a smaller, manipulated version of a tree and need the same environment and conditions as its larger counterpart. It is not a different species, just a smaller version by manipulation. So in short, they are not meant to be indoor plants/trees, you'll have to abide to its natural preferences if you want it to flourish.

Most Bonzais are kept outside like any other tree. The one guy that we used to get art classes from probably had a 100 or so bonzais in his back yard. They don't do very good inside unless it is by a window and gets a lot of sunshine, which again will have a negative effect on the tarantula in this case.

Might have to use artificial lighting or create a specific hide with excellent ventilation for the T as it will get very hot inside of that glass enclosure if it is put in the sun even for short periods of time. Think green house.