Hello Swap,
"Does User Apex Subscription automatically entitle us to use Anyconnect client ?"
User Apex subscription is about the client itself [ Anyconnect 4.x].
"If User Apex Subscription is purchased on subscription model (e.g. 5 years), what happens after 5 years ? Can user still connect , or is it a hard limit?"
OP> Yes you can still connect but you are not entitled to use the software anymore until you refresh your license.
"If we use Windows 7 native client to connected to FlexVPN server on ASR, do we still require a license on ASR ?"
OP> As long you have at least the securityk9 license, there is nothing else you need.
"With FelxVPN on ASR, does Windows 7 Client have an option to use Group Username/Password or is it only for certificate based authentication ?"
OP> 2 possibilities - RSA-SIG on both or a CERT on the router + EAP on the client [ per RFC5996 requirement]. EAP need to be terminated on a radius or if you run latest greatest you can use AGGR-EAP with local user database.
"is there any licensing for Mobile users ?"
OP> only on ASA as far as I know.