You cannot order a Motability car within the scheme rules until invited, THREE MONTHS before your lease is up. As I said,and you have now confirmed, your lease ends sometime in March, therefore you can order through Motability with a fixed AP on a specified date in December.
Anything else you arrange is outside the scheme and at your own risk. As we all know any car can be removed from the scheme at any time before your permitted ordering date.
By all means enjoy investigating car options now, but rules is rules!!