I get a cup/jug of boiling water and dip the end in for 15/30secs then push the tubing over the barb. Once it is all the way on and cooled down it is stuck fast (I have always used the XSPC barbs mind, they are longer than the rest I have seen).
To bleed I unscrew a barb on say the pump at the bottom of the loop and catch the water in a bowl. Then you have to twist the tubing up so when it uncoils it screws itself back in - then you tighten it up with a spanner. OR, just cut it lol. Depends how I feel at the time.
As for tubing OD, it is up to you mate. If you use 1/2" tubing you MUST use jubilee clips. 7/16" you don't and it is supposed to be more flexible than 1/2".