I would advise you to get as physically fit as you can before surgery, but with it being on Monday there's no time. I say that because the more you can walk after surgery the better you will recover, and also because it is surprising how much you use your abdominal muscles in everyday life, and they do hurt for a bit after the surgery. Having the strength in your arms and legs to help move you around is good.
I had keyhole surgery and it was fine. I had discomfort on and off rather than excruciating pain. I was careful to obey instructions not to lift anything heavy for 8 weeks post surgery, just to be on the safe side. I could probably have done a bit more than I did but it was quite a good lesson to my DH in just how much laundry he generates.
I had no digestive problems afterwards, bar the usual post-op constipation for a few days. I can eat more widely than I did before surgery. If I am away in a hotel and eat a full English breakfast and then have fish and chips for lunch I might feel a bit bilious but that's the limit of it for me.
My stones caused pain on and off for some 10 years but the pain was initially only about once a year and I thought it was just really bad wind. I only once had pain so bad I got palpitations from it, and a few times had pain that made me cry, but nothing that had me running to A&E. The worst pains came on in the 6 months before I had it removed. Luckily we have insurance so I did not have to wait long because once the pain ramped up it happened more often, too, despite me being very careful with diet.
I am hearing horror stories now with people being denied removal over and over again and they are in agony. I doubt this will get better any time soon so in your position I would go ahead. If it has played up once it will likely do so again.