well first off the big B for budget how much have you got to/want to spend and do you alreayd have a new head unit as that will can eat up lot of cash if you want all the bells and wistles or be qute cheap and still get the job done well.
if you dont have a headunit already , what do you want/need form it and doubel or single din.
usb , probably thse days , bluetooth if you own a phone then yes, sat nav ???
single vs double tbh the double looks way neater than any facia plates imho and doenst need to cost that much more.
dont want a huge box in your boot , that basically limits you to eith bin your spare wheel or pull apart the entire rear interior and get the bose plate out but either way its gonna have to be a custom box.
so when your done wiht that lot post up and we can get started