I have not found anything about the XLATES, but the following gives you the basics about how many connections for all the ASA5500 series devices and what their basic capabilites are.
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You can use the "show resource usage summary" or "show resource usage resource Xlates" command on the ASA to see information about ASAs own resource usage and limits.
As you are using single public IP address for users with PAT translation I think it limits the connections
65535 as thats the maximum amount of ports you have at our disposal for PAT translations. Not sure if thats the exact amount.