The Maxxis High Roller you've bought should be fine, Maxxis are pretty reliable tyres to use when converting to tubeless. I've run one before in a setup with some sealant, and it worked just fine.
Pressure wise, don't get too carried away trying to run mega low pressures straight away. Dropping 10psi in an instant could lead to lots of dinged rims potentially! Best to start at the same pressure you used before IMO, then once you've ascertained that you could go lower, maybe try 2-3psi less, then if you feel you could go lower still, try another 2-3psi less. Don't just jump straight in with a 10psi drop, you will likely knacker your rims!