Oh my goodness... That clover leaf layout is just amazing. I so badly wish I was premier! I would implement that no qualms at all... It's a huge cost, but so badly needed.
A subway is perfectly viable for parts of Brisbane. If it was high speed, cheap, clean and reliable it would be an absolute hit. I'd use it constantly for commuting in inner suburbs (presently I rarely if ever use PT).
The southern loop probably wouldn't be constructed for some time. The roads down there are better and public transport marginally so. The other 3 would be so beneficial though.
Some well thought out subway/surface rail and subway/busway links would also be very handy indeed. Especially if the &$#*@ Go Card was working properly.
Edit: Nope, you have the interchanges sorted just fine
. The East/West loops could be implemented ASAP, followed by North then South.