Its good they are at a hotel and not in your home, for first things. This is absolutely bound to be a tricky meeting at best. Old emotions and angers, and new expectations; you're strangers and yet you are related. In your favour is that there is goodwill and the will to make it work.
Try to keep low expectations. It may not pan out even if you all want it to. Keep it low key and if its not too late, don't build up your son's expectations. Anything that goes well is a bonus, not a right. After all - you are strangers now. Its an odd situation (one I've been in, btw. Complicated family history, in spades).
I think one of the keys here is to both agree on how much time you spend together, preferably ahead of time at least for the first meeting.
I would suggest keeping the first meeting relatively short like an hour or two and considering even the first meeting in a neutral place like the hotel bar, unless it feels really right to ask them immediately to your home. In your home, its going to feel odder for you perhaps. He's your absent father who really should have been there. Meeting in neutral ground allows you better to meet as adults not father-daughter ... becuase the bonds are there, but also half-broken. Then go home for lunch and let them have lunch there, unless you really suddenly click amazingly. That space and time apart will give each of you time to take in first impressions and to come to terms with things. ALso, they must be rather older now and they may need to rest after the long journey. I would suggest this to them now, ahead of time, so that it doesnt come as a sort of rejection.
then meet up again early afternoon and go to the playground if they like that sort of thing. They're there for your son perhaps more than for you, so it's grandparent / grandson's time.
If things click then they can come to your house for dinner maybe? if not or if they need to rest, then Im sure they can eat at the hotel. Would you ask them over in the evening to chat just as a more grown-up conversation after your son is in bed?
then sunday morning, meet up again.
None of this needs to be written in stone, if you find you get on like a house on fire then maybe no need for breaks at all.
Btw, I know its incredibly sad if a child has no involved grandparents. But in a way, the child himself does not know fully know what he is missing and can accept it if you say "I'm afraid mummy's family wasn't always very nice so we don't see them very often". But it is of course much, much, much nicer for them to have an involved grandparent!
Do you cut people out too fast? I dont know. I think that it sounds sensible to focus on people who bring happiness, not negative drama though. Constructive people are so so much better to be around than negative and leave a far happier long term impression. So I suspect that your approach is sensible.
if you find yoru own feelings about his abandonment surfacing, then keep in mind they are there for your son more than for you, actually. Also, be sure to pay equal attention to both your father and his wife as far as you can. That will send the message that you accept them both equally. Nothing is going to go bad quicker than ignoring her. She could be a powerful force on yoru side though, if you get on well with her.
very best of luck, its a very exiting time ! Would love to know how it ends up :)