First of all, best of luck and hope you have a wonderful visit! Look forward to your thoughts.
The Habitat Africa - The Forest building is small; if you hang by the crocodile you might not quite see what's going on around the corner, but once you turn away from the crocodiles, everything is pretty visible at once. When waiting for the pangolin I've been able to watch the duiker, okapi, and sengi enclosure (not in use at the time) without losing sight of the pangolin area. My last visit to that exhibit, the keeper did announce himself before entering the bts area to start the feeding. I'd probably recommend being there a little before 3:30 -- it's usually about that time but does occasionally dip early. The sengi are right across from the pangolin so if they're visible you should see them!
The echidnas are very show and easily seen. There is usually one in the day room exhibit and two or three in the nocturnal area. The wombat are across from the echidna and somewhat more shy. I probably recommend doing Australia and Desert's Edge at the beginning and/or end of the day for your best shots at seeing the wombat and the genet, who I had really good luck with one one visit and missed on a subsequent trip. The genet is near the sand cat and beat-eared foxes if that helps in any way, although unlike the above examples you can't really view multiple species at the same time.
Tropic World: South America is not super consistent and for a while seemed empty every time I visited, but on my last visit I did see the anteater, tufted capuchins, squirrel monkey, sloth and spider monkeys all out at the same time; the crested had not arrived yet. This was around 1:20p in the afternoon if that is any help.
The pachyderms should be easy, I see the tapir and pygmy hippopotamus on almost every single visit. They are both in large enclosures though so may be a distance away. Banana (pygmy hippo) is a pretty active individual and there are two tapirs right now even if one or the other is not active. The capybara and a single black rhinoceros are also still present, but the capybara can often be missed. The interior of Pachyderm House is closed to the public now and some of the former exhibits are fenced.
I hope some of this helps.