That's a lovely cake!
I'd cut a slice out of it as if cutting an ordinary round cake then lay the slice on it's side then cut it into portions!
But however you cut it I'm sure it would taste delicious
It appears to be simply single(?) layer tiers stacked, with the top tier 3" or 4" tall, so I say cut it just as one would a wedding cake.
If you make the tiers single layers you would not need any support between those - just support the top tier. Then you can cut those single layers into 2x2x2 pieces around the outer parts before getting to the 4-6" part so you would switch to 1x2x4 cuts. HTH