Are you able to turn wrenches and do the work to put it together yourself? IF not, I would just talk to a New Holland dealer (more costly but easiest way to get it done.)
What do you need the remote to do? Raise and lower (double acting cylinders?) or continuous power (backhoe / log splitter?) or run a motor? Also, how many remotes do you need?
Your tractor is "Open Center" but I do not know if New Holland uses "Power Beyond" or is just open center. Do you have a front end loader on your tractor?
If not, it's not impossible to add remotes - just a whole lot more work!
If yes for the loader, that valve/spool will have 2 lines for the lift, 2 lines for the curl, how many extra lines are there? Is it just 2 more lines (Power In and Return to the tank) or is it 3 more lines (Power In, low pressure return to tank and Power Beyond)?
Welcome to the site... the more information you can tell us the more we can (try) and help you. (I don't know much about New Holland but hopefully someone else will chime in here....)