mvc json format yes or no

I have mvc / razor app using ajax to make some transactions. everything is working fine.
But just we will add more parameters in data and It is going to super long list. so I want to find better way to handle this codes below.
I am thinking using json format passing value from front to the back. but do not know how to do it.

my question is:

1. is it best practice to use json format to pass list of value back and forth? If yes, can you show me how to do it with my codes below?
2. If json is not, can you suggest me what to do?
3. On the end - code behind. I do have lead class. and hope the best will be JsonResult CreateLead(Domain.Lead l) so I do not have to worry too much about list too long.


Thanks

$.ajax({
                                url: "/Home/CreateLead",
                                datatype: "text",
                                data:
                                {
                                    'firstname': document.getElementById("first-name").value,
                                    'lastname': document.getElementById("last-name").value,
                                    'phonenumber': document.getElementById("phone-number").value,
                                    'emailaddress': document.getElementById("email-address").value,
                                    'totalcountadult': document.getElementById("total-count-adult").value,
                                    'totalcountkid': document.getElementById("total-count-kid").value,
                                    'pickupdate': document.getElementById("pickup-date").value,
                                    'dropoffdate': document.getElementById("dropoff-date").value,
                                    'fleetid': '@Request.Url.Segments[3]',
                                    'eventname': '@Request.QueryString["eventName"]',
                                    'currentcitystate': document.getElementById("current-city-state").value
                                },


[HttpPost]     
        public JsonResult CreateLead
            (
             string firstname, string lastname, string phonenumber,string emailaddress,string totalcountadult,
             string totalcountkid, string pickupdate, string dropoffdate,string fleetid, string eventname, string currentcitystate
	    
            )
{
return Json(l, JsonRequestBehavior.AllowGet);
}
  

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