If you will be using rear remotes to run the grapple then you'll need two hoses of 3/8 or even as little as 1/4 with appropriate adapters to fit your rear remote outlets and long enough to go under the tractor, up the FEL post, along the FEL arm and terminate at the bracket you are building on the FEL torque tube (cross piece). Obviously you'll also need the hoses from the grapple arm cylinder to come back to the FEL mounted bracket. Again, 1/4 inch lines are fine though some use 3/8.
To measure the length of hose needed from the rear remotes to the FEL bracket I suggest using an old hose and literally "install" it so you can judge how much extra to leave for bends (especially at the bottom of the FEL post where the hoses will need to turn 90 degrees from under the operator station. Don't make the bends to sharp but route it and secure it so that it won't be snagged by brush. I used zip ties to hold the hoses tight to the underside of the operator station. I should have mentioned that it is nice to get 90 degree fitting adapters installed at the back so the hoses fit flush against the back of the tractor and that you don't need to have a big loop of hose sticking out the back before it travels over the left rear axle and under the operator station.
I found the process of measuring and figuring out how to secure hoses to be much easier once I had "installed" a garden hose in exactly the route I intended to use.
Be careful to determine exactly the right type of fittings. The tractor rear remotes will almost certainly be 1/2 inch Pioneer style female so you'll need male fittings for both rear connections. If you are using 1/4 inch hose you'll need the appropriate adapters to go up to the 1/2 inch fittings. At the grapple end you'll need to determine whether you have SAE or JIC connections to the hydraulic cylinder and get the hoses made up appropriately. You have your choice of what fittings you want to use for the connections at the FEL bracket but I'd suggest sticking with Pioneer quick connect style in either 1/4 or 3/8.
You can get all this stuff from internet discount suppliers and that is definitely the cheapest way to go (you'll save at least half). However, and this is a big however, it is very easy to get confused with what types of fittings etc if you haven't done it before. It might be a good investment to work with a local shop that can make sure everything is compatable. Again, the main thing they need to know are the lengths and the exact type of fittings on the hydraulic cylinder. I'm pretty sure you have 1/2 inch female Pioneer quick connects on your rear remote as that is industry standard.
There are lots of guys that have done this so just ask questions if you are unclear.
