welcome to the forum Mox50

I am sure its quite possible to 'go it alone' and I know there are forum mebers that would do just that ... but its not something that I would do.

You have to know what you are doing , if you are used to cooking very large pieces of meat on a BBQ or over a fire pit , then fair enough , but if you are not t,hen what you have to remember is that 30 to 40 people is a large number of people to feed and if something goes wrong it will be a huge problem.

If you get a company in to do the hog roast , they will come along and it will all be relitivly hassle free for you , everything will be ready prepared  , you will know that it will be well done and well cooked, you will know that the firm will have adequate insurance just case anything goes wrong.

Being vegetarian I have never had a hog roast , but , I have a meat eating family and so am used to cooking meat , I know that some of them have had hog roasts at weddings and the like. As far as I know they were cooked by a profesional.

Sorry I havnt been much help.

We do a pig roast on a spit. A spit can be a great thing to have if you have the room to store it.  We mostly make spit roasted lamb but have done a whole pig before.  Can't remember how big it was but it fed 20 people with a fair amount of left overs.  We did however have plenty of side dishes which I assume will be the case for you too.