Can you buy less than 1 bitcoin?
Yes, it's very divisible,
https://bittylicious.com/ is good if you want to chuck a few quid in.
Can you go short bitcoins are you just buying and holding actual coins?
Yes, you can go short via exchanges. just google it
I thought there was a fixed number of bitcoins? How does mining work in relation to this?
Yes, the block reward for the successful mining was 50, then 25, then 12.5 see here
http://www.bitcoinblockhalf.com/Are the competing currencies the same thing just with different names?
Some are just knock offs, generally to do well they have to add value somehow, ethereum and others allow smart contracts to be build and are quite different.
Whats the driver for meteoric rise of crypto values?
Escape from fiat currency via capital flight, increasing confidence, user adoption, business adoption, Japan recognizing bitcoin as a legal method of payment, coins being taken off the market for sale, people buying to speculate, high profile individuals declaring positions, likely more reasons but everyone thinks differently.