Well my opinion would be to go ahead with your design. Keeping it simple is the key only configure MST or RPST if you know what your doing with the config. PVST+ is simple and enabled by default. And as you say it is a Datacentre, i believe your design would be final in these cases just go ahead with PVST+. Use VTP transparent mode on all your access switches. This way you can keep control of the vlan information passing to your access switches. The core can run on VTP Transparent too.
Redundancy is an important factor. As you have mentioned you are using your 6500 as core, just another question are you having a single sup or double sup engine?
For your HSRP do load sharing across your core switches odd vlans given higher priority in Primary Core and even vlans given higher priority in Secondary core. Similary do remember the spanning-tree priority command.
For example vlan 10 which is having higher HSRP priority on Core Switch 1 should also have spanning-priority lower i.e probably keep it as 8192 and this spanning priority for Vlan 10 on Switch 2 should be 16384. Load share your layer 2 also across switches.
HTH
Hoogen
Do rate if this helps :)
