He's very young, and was taken from his mother far too young (around half the age he should have been at seperation - I know this is not your fault, his mum was not there, but it's not his fault either!) and as a result he hasn't learned important lessons from mum and siblings about play and hunting - the most important being 'how much is too much'
I have one who is similarly inclined, he's now 2 1/2 and has never completely given up his foot-hunting obsession. The best thing you can do is ignore it - we wore wellington boots around the house for months on end so that we didn't react when he would claw and bite our legs and ankles, and many is the time I've shuffled down the hallway with a cat clamped upside down on my leg. The others I have that were separated from mum at a later age (around 13 weeks) have never even attempted anything of the sort and are much more gentle, they know to retract their claws and not bite.
Besides ignoring it, the best thing you can do is provide interactive play to tire him out and fulfil his need to practice his hunting skills. Watch his body language so you notice when he wakes up and needs something to occupy him, and get the toys out - wand toys, toys on strings, toys to throw - as long as all play encourages him to stay away from your hands and feet. It is a good idea to play before mealtimes as it simulates natural hunt->eat behaviour.
Please do not spray him, he could get an ear or eye infection or become fearful of you, you would not spray a human infant for crying so please don't spray your kitten! You just need to keep him busy and work off his energy.
Do you have any other cats? An orphaned or too young kitten can really benefit from having a similar aged playmate so they can learn to play together without being too rough, as long as both are vaccinated I would recommend getting him a friend - it will take the focus off your legs as his main plaything