'Most' the bolts you’re going to be removing need to be torqued to 25Nm (a couple may be up to 45Nm) and the lowest is about 10Nm.
For normal engine work you would be better off with a 3/8" size torque wrench (the 3/8" is the size of the square fitting in the socket).
A typical 3/8" torque wrench does from 10Nm ish up to 60Nm, e.g. the Halfords one
click here 
Obviously you need 3/8" end sockets to fit the torque wrench, or an adaptor to step down or up from the size of your sockets.
With sockets, you get a few different size of end size (i.e. the size of the square in the end of the socket that you fit to the ratchet) - you get (smallest first) 1/4", 3/8", 1/2", 3/4" and 1". The size of the end depends on the size of the bolt your undoing, and the torque that it is done up to.
For most engine work you will need 3/8" mainly, but a 1/4" set is also handy at times if space is limited. For more complicated work (or stuck bolts) a 1/2" set (even part set) is also handy. A selection of these three will do most engine work for you (in fact, that's all I use at home!)
(a 1/4" is handy for undoing Jubilee clips!!)
There are times, for really tight bolt, where you need a longer breaker bar, a 3/4" set is useful, but I just borrow these as and when I need them, which isn't that often.
Without plugging Halfords too much, I don't know what tools you've got had home, but IMHO you can't go wrong with a Halfords professional set.
With one of these you will have all the sockets/spanners you need to do most jobs on your engine.... there decent quality tools (for the money) and they have a lifetime guarantee.
click here (And they are on special offer at the moment).
The only other tools you need then are a screwdriver set, a set of pliers and cutters etc, and a 1/2†breaker bar is always handy!!
You will also need a viscous fan spanner, to get your fan off.
Sorry if any of this post is teaching you to suck eggs…..
Ian
