1st to TS are you having 2 lines or just that one line that you are using in your Ip5, if the later please beware as the other bros had said taking the sim card in and out is quite inconvenience unless you have the poking pin with you all the time.
2nd question is do you still need the phone functions (ie. call, sms, mms, messaging n chat) if so currently the info leaked for ipad mini 2, saying that its still does not allow phone functions, yes for certain (not ALL as per some bro said) can be gotten from cydia, provided you are willing to jailbreak (though a simple process but still need to decide as will void warranty unless before you send to warranty you flash back to original rom again).
3rdly, what is the function you are planning to use your future ipad mini 2 for? for watching online shows? for reading? or gaming? and the duration of such functions on the ipad mini 2 per day. Why i am asking is becos i think by now you will know that there is such a thing call hotspot from your ip5. if the duration of ur ipad mini 2 activities are not long, its still more advisable to just tether by hotspot.
If the ipad mini 2 actvities are long then it will not be possible as the battery drain on the ip5 will be too great unless you have a external battery handy.
lastly are you planning to sell or trade in your ip5 to get the ipad mini 2 and revert back to a older phone?
Hope this helps.