Question

Does the Pokemon with compoundeyes have to be first in your team to increase the item chance?

Answer 1

If the Pokémon is in the lead spot, chance of encountering a wild Pokémon holding an item increases

Source

So Chansey is a little more likely to be holding that egg you want. Of course, it's also more likely to be holding an Oval Stone.

It increases by 50%
Source