One question - do I plant the tank early or wait 3-4 weeks until the amazonia II has been cycled in?

My local store recommended me to wait, however, have had conflicting reports to plant densely straight away.

I'm looking plant Monte Carlo (carpet) and something in background of my iwagumi.
Any suggestions?

Why not do what ADA recommends. Plant immediately even before the tank is filled. Some of the content in the link below you won't have or might not need, but it will give you good information on how to start up successfully.

http://www.adana.co.jp/en/contents/process/index.html

Definitely plant right away. Not only will the plants use up a lot of the nutrients released, they'll be more grown in by the time your tank is ready to house livestock.

The link @Asteroid shared is a good one. You'll experience less ammonia leeching than you would if using regular Amazonia, so fewer water changes may be necessary.