>>35792985When you're doing species changes all the pokemon should use national dex numbers from bulbapedia until at least gen 5 (what essentials supports, they might be using the gen 6 expansion, with gen 7 etc they'll probably just you know only insert pokemon that they actually need so the numbering is probably off for gen 6 and gen 7 but the cries audio should give you an indication of what numbers they have because pokemon cries MUST CORRELATE with the pokemon number).
For items, any new items are probably tacked on afterwards but you should be able to use any core items from the default pokemon essentials pbs you can download off the Essentials wikia.
When doing a search use 4 bits unless you're doing something like EVs (in which case you probably want to use unknown initial value and then search for increased values)
Backup your save file before making changes in case of any nasty surprises in future updates.