Thanks for the help guys, if I take a shield as well as light armour would that not be a good idea? As I will still get a save agaisnt S5 and anything less than that is 5+ which is pretty good for 5pts when you have a parry too - just realised shields are free so I have to take those. And with 5 man ranks a spear wouldn't really do much, just an extra 5 attacks that aren't likely to do much.
Would spears be more viable in a horde of 40+ models? As I would get 3 ranks anyway because it is a horde and the spears would then get me an extra 10 attacks, but then I guess that is potentially another 10 warriors that I could take.
You always have the shield, but adding light armour is a pretty bad idea: its adding cost to a cheap model whose principle bonus is being cheap. A 5+ save is nice if you are fighting S3 but then anything S3 will be struggling to get through a unit anyway so it isn't really that impressive. S5 would totally ignore any armour save a skelly could get...
I think that no matter how many skellies are in the unit you probably only ever want to be using it 5 wide. That'll give you as few model in B2B with the enemy as possible and limit the damage you'll take. With that thought in mind taking HW+shield is the best plan as it makes them the bet tarpit unit you can.
Hoarding them up and giving them spears makes them a half decent attacking unit but that'll only be effective against weak enemy units. Also the spears are only really helpful in prolonged combats since you can't use them if you charge (and if the enemy charges you chances are they're confident they can beat you anyway).
Overall- I think it depends what you want the unit to do. If you want a tarpit then build them as such, if you want them to be able to put out a relatively high degree of damage take a hoard and spears (but skellies are never going to be devastating).