Can I change the amount of hard drive space i have allocated to Ubuntu later after I have installed it? I'm not sure how much I should allocate as I wont be putting many big files on it... How much would you recommend if I have 2TB/Windos7
Yes you can. Easiest tool to do so I find is gparted, so if you think you need to add more space or you need more space in windows you can do so on the fly.
Just search for 'gparted' in the software center.