People’s doses are all over the place. 300mg is common but people also take 400mg or more. Keith (the site’s owner) advocates the maximum dose which would be 800mg or 900mg but I think that would be pointlessly risky in most cases. In most cases, no allopurinol dose will completely prevent symptoms during the first months.
Some people apparently get no obvious side effects even at the maximum dose. On the other hand those of us who do not take well to allopurinol can get side effects from very small amounts.
As to staying off one’s feet… well, that’s another way in which people are different. You’ve got to figure out what works and doesn’t work for you. It also depends on what drugs you take to suppress symptoms.
Personally, I try to avoid doing painful things for most of the day. I think it’s not controversial that you shouldn’t be completely immobile for long periods but during severe attacks I would lie down most of the day, use crutches, avoid regular shoes if putting them on is painful and so forth.
The main reasons I’m very careful is that I do not do well on many common drugs and that my attacks tend to come back shortly after fading away and I find rest makes that less likely. Others have no such concerns and find moderate weight-bearing exercise helps their feet go back to normal quicker.