Im not experienced in GNS. What simulations are you referring to? Why not rent some racktime from vendors that support CCIE security? I would imagine they would give you lots of equipment to play with.
Probably. SECURE for sure. On the FW they say that 8.2 is what is tested but only 8.0 (and lower) will run in GNS3. You may want to look at rack rental or picking up a 5505/5510. How soon are you looking to do them?