Piaow, for an overhead reel you want it to unwind off the mono spool just like it goes on the reel spool so the mono reel needs to run on an axle if you get what I mean. The line also needs to have some tension applied as you wind it on. Of course you need to make sure it goes on evenly across the spool too and the only way to do that is to guide it with your thumb. I use the rod to keep an even (sort of) tension on the line and have made pukka tensioning methods using a screwdriver (axle) a spring with a washer either side - one against the screwdriver handle the other against the mono spool - and the blade end of the screwdriver in a vice. All pretty hairy and dodgy but it works. Getting your reel spooled in the tackle shop is you best bet.

There are some respoolers for sale on trademe they dont cost much.The spool fits on the gadget it has a tensioner on it then you clamp them on to your rod or somewhere else and start winding

Late post I know but due to extreme cabin fever etc was trawling.
I've always spooled up my reels by threading the line through the rod and dropping the spool into a bucket of fresh water. The water creates it own "drag" to some extent and stops the spool from overunning if you slow down your winding.
My rule of thumb for line pressure is my thumb. As you feed the line onto your reel I hold the line between thumb and forefinger so that any water on the line is shed, things can be somewhat easier if you have a level wind reel.
Works for me.

Sit down, put a piece of dowel through centre of line spool, place on floor, put feet on dowel and apply pressure while winding the line onto your reel. This is the method recommended by fly fishing guru Peter Morse for putting the braid backing on fly reels. This will work for your mono too. You just adjust the pressure with your feet. Piss easy and sorted!