You definitely need to do your homework here. Rights of way across other people's land can be a nightmare and I have first hand experience of it.
Get one thing clear in your head. The planning permission for a track is completely unrelated to any rights of way. You can have one without the other and vice versa. You need both.
Not sure how long planning is valid for I thought it was three years. But the work only has to have been started and it's valid forever I believe. ...I too have planning for a new track to my house (so I can get rid of the current route across my neighbours land) to avoid the planning running out I built the new entrance onto the road. Financially I cannot afford the rest, but it can wait forever now.
Next the right of way. You need to check one exists, and if it is vehicular because that's what you need. Presumably the route is their now and could be driven in a 4x4 in dry conditions ? You say there is more than one landowner. Essentially if a vehicular right of way has been granted or exists you have the right to install it and maintain it, this is easier said than done. But what is its exact route, how wide is it , are there any restrictions on its use. Chances are a right of way exists, but from the days of horses and carts, landowners might well resist an upgrade. One of the key things is will the other owners be happy ? Will it be /can it be fenced or wiill your nice new track be churned up by cows and tractors all winter ?
These are my immediate thoughts.
I use a forum called garden law , some very knowledge people on their regarding planning and rights of way. I suggest you post your issue there, but you will need to include more detail.
You must do your homework before committing to this one.
When I get chance I will dig out the quotes I've had for my track and turn it into a rate per metre.