Mastering files of different sample rates

Hello Cubase users
I’ve got a bunch of Christmas carols files recorded over the years that I’m trying to mix down to a three-hour play list.
Problem is, the sample rates are different. Some are at 44.1 kHz and others are at 48 kHz. The bit rates also vary from 16-bit, 24-bit, to 32-bit, and there are some mp3 files among them.
Is there any way I can import them into a single Cubase project to master them (add reverb, limiter, etc) and have them all playing back at the right pitch? At the moment all the 48 kHz songs are 1.5 semitones flat.
Has anyone got any ideas?

Obviously you need to convert samplerates.

OK. I’ve just noticed that there is an option to do this when I import files. So I guess that’s how to do it.
Can I ask one more, pls.
I am using the Stereo Mastering Preset available in the Hub. It is asking to convert my files from 32-bit float to 16-bit when I import them. Should I convert them down? What’s the advantage in that?

Nothing - leave the bitdepth just as is.

Thanks then @svennilenni