If you're wanting to keep it reasonably cheap, a full chainset (BB, cranks, chainrings) would be the cheapest way to sort out the front end, plus a 7/8 speed chain and 8speed cassette and you're sorted. Deurallieurs/shifters are likely to be fine, if in any doubt visit the LBS before you spend anything! An external BB will work on your 73mm shell, most modern shells are 68mm and use 2x2.5mm spacers to allow tweaking of the chainline. Square taper BBs are still readily available.9/10/11 speed chains and chainrings will work on an 8 speed setup, but wear faster, be less durable and shift less cleanly.
Good to know that 9/10 higher speed chains will work if need be, will get an 8 speed one if they behave better and last longer.