You'll probably find responses here vary considerably!
Fibre I started shortly after the my takedown, as per my surgeon's recommendations, but Metamucil gave me increased gas so I eventually stopped it and switched to Benefibre. I took that for a while, but after time I decided it really made no difference either way so I no longer take a fibre supplement regularly.
Immodium I have never used on a regular basis. Like mgmt10, I was told not to use them at first (my surgeon said not in the first 4 weeks, partly because I had been prone to obstructions), though after that my surgeon told me I could take up to 6-8 per day. I find I don't really need it. That's not to say I never take imodium. I do use it when I need it (i.e. if I'm having very liquid bms), but mostly I use it prophylactically, such as before a long car ride, once when I was a bridesmaid, etc. At most I've probably taken 4 in a 24 hour period.
Probiotics I didn't start using until a year post takedown, when I got my first (and so far) and only bout of pouchitis, because up to that point, no one had ever recommended them to me. I now swear by them and would never skip a day. I wish I had known about them sooner.