I would work on building trust with the bird you have now before getting another. Even if you get a hand trained bird, you still have to get them to trust you; depending on the bird that can be a week or several months. I have two hand trained birds, one was my buddy from day one, the other is just coming around after several months.
Save and get a bigger cage. I have a single flight cage and it is excellent for two birds. Emily was in it alone for several months and loved it. I wouldn't worry about the transfer to much. It all depends on the bird. Emily was cautious but only took a day to adopt; Heneri knew a good thing when she saw it and I couldn't keep her out.
They will know what to do with a cuttle bone and only nibble on it as needed.
Welcome to the forum!
"Many have forgotten this truth...You remain responsible, forever, for what you have tamed."