Hello SanRazo618. Well, it all depends on space. The bigger the enclosure, the less problems you will face in interspecific conflicts, although realistically, those type of habitat require incredibles amounts of money to maintain that might result in non-profitable for the zoo management, although you said is high budget so that shouldn't be a problem at first, but maybe in the future, in terms of realism.
As well, It also depends on the population size of elephants and other species inside the enclosure, and the characteristics of the later, and also the sex of those animals. Male elephants can be extremely aggressive during mating season, specially young ones, so building an area where they can be separated from the other animals and the herd if required is highly recommended. Moreover, in what respects to which species are more suitable to share habitat with, I would suggest those that are small and fast enough to avoid the possible wrath of the elephants, but not too small because thay can also be stomped by them.
Also, consider adding certain areas on the habitat where elephants can't reach but the other species do. This will aid them to avoid the elephants if needed. Some examples of species I would consider are: zebras, medium size antelopes (from a Thompson's gazelle size to maybe an impala or nyala), birds like Guinea fowls or crowned cranes (but leaving them the ability to fly), wildebeest, etc., but never place animals that are usually aggresive, such as buffalo, rhinoceros, hippopotamos or larger antelope species. In the same way, avoid placing giraffes, because they can get in serious danger of falling and hurting themselves (or even worse) if an elephant decides to charge at them. Nevertheless, I suggest you to have a look at the AZA husbandry manual, they usually explain quite well the best animal combinations possible.
To sum up, as I said, it all depends on the enclosure size and its design, and aggressive species must always be avoided. If done, no problems should be encountered.
I hope my answer helps you.