Well, you'll need a machine. But before that you should really ask yourself a few questions

How large will the operation be? Will I only offer only espresso based drinks? How capable are my crew? How much space have I got? Am I doing this for the money?

Now you may think that the answers to these are self evident but you should bear in mind that the vast majority of coffee sold in the UK is not espresso or needs to be espresso based. You should also bear in mind that while it is not rocket science an operator does usually have to be trained to use an espresso coffeemaker therefore the amount of automation in the process can be critical.

What type of machine?

Fully Automatic. These come in a variety of styles, the basic machine will automatically grind the coffee and brew the cup, as sophistication (and cost) increases so does the ability of the machine to process milk based drinks without operator intervention. At the finest these become deluxe vending machines in all but name!

Automatic. This is the traditional portafilter machine with a timer attached to the water supply. Once programmed this ensures that at least your cup will not runneth-over if you get distracted. Being honest it is not worth trying to save money by not specifing this, you can do other things (steam some milk, prepare the next coffee, nip out to the post office?) and not need to worry about the coffee once it is started.

Semi Automatic. Why these machines are called semi automatic I do not know. I suppose that the machine does look after itself in the temperature and pressure stakes and therefore all you've got to do is switch the pump on and off. Anyway they are not worth the saving (~£100 per group) so don't say I didn't warn you!

Part Two - Inside the beast!