I personally would never make the decision for my birds to have them share a cage. Especially if they were different species.
If *they" decided to share, I'd still keep the second cage set up for times they needed space apart.
Imagine your landlord bringing a total stranger into your house and telling you that you have to share your bed with them. Not just your house and your bedroom, but your bed.
To me that's what we are doing when we try to make birds be friends/mates.
It's taken my current two birds a little over a year to be friends, and there is NO way they could safely share a cage.
I agree with others that have suggested it's healthiest for everyone if you do not assume the two birds will be cross-species cage mates, and prepare for separate housing for each of them.
I volunteer at a parrot sanctuary where quite a few of the birds are best friends, and preen each other all day long, but we still have them go to bed in separate cages. Only the same species pair-bonded birds get to share cages.
All that said, have fun finding and meeting a new addition! My two are very different from each other and it's been a lot of fun helping them become friends
