I know it's late - you may not need any answers here but maybe you'll find them helpful regardless.

Hi all, i am about to sew my curtains for babies room. I am a novice sewer but have done some before... many years ago LOL
I am very much in need of some guidance!

We have bought 100%ployester backed curtain material, with the 'stuff' up the top for the curtain hooks (yes i am very technical)
Usually called curtain tape, specified as various types - pencil-pleat tape, lining tape, tape for normal weight curtains versus sheer curtains etc. If you go somewhere they sell tape and look at the boxes, it'll show you the kind of effect the tape can produce. Most commonly it's a choice between pencil-pleat (standard pleats, like |||||) or triple-pleats (3 pleats-flat space-3 pleats, like ||| ||| |||).

When it's pre-stitched to the curtain fabric, it is almost always pencil-pleats.

What needle will i need to use?
Machine sewing, standard needle. Hand sewing, sharps in a size you're comfortable working with.

How much Hem on the sides do i leave?
Side hems are usually around 1.5cm But you can do wiser or narrower as it suits you. Wider can give the side of the curtain more weight and 'stiffness' which can help it hang neatly and not be blown around quite so much if the window is open and the wind comes through.

And If you have full length curtains, how far from the floor do you hem them? DH was thinking around 10cm off the floor, but i am not convinced!!!
Whatever you want. Floor length is usually considered 1-4cm from the floor. Standard process is to hem the sides, hang the curtain and them pin it to the length you want - this also helps you get it even and be sure it is the length you want.