If you can patch both WAN ports into a switch that can speak VLANs (dot1q) and trunk them to int 0/0 and create subinterfaces as you've done with int0/2 and tag correct VLAN, that will get round your lack of ports.
To failover between WAN links look at IP SLA such as below.
route primary-isp 0.0.0.0 0.0.0.0 1.1.1.1 1 track 1
route backup-isp 0.0.0.0 0.0.0.0 2.2.2.2 254 - high admin cost
track 1 rtr 10 reachability
sla monitor 10
type echo protocol ipIcmpEcho 1.1.1.1 interface primary-isp (Example I am pinging default GW address)
num-packets 3
frequency 10
sla monitor schedule 10 life forever start-time now
If you're PAT'ing for outbound traffic you will need to make sure you configure for the backup ISP
Example
object network Inside1
subnet blah
nat (inside,primary-isp) dynamic interface
object network Inside2
subnet blah
nat (inside,backup-isp) dynamic interface
Here's an article http://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/118962-configure-asa-00.html
Joel