I don’t have any experience with your first question in that I’ve never seriously tried to do an entire album within one Cubase (or any other DAW) project. It feels to me like that would be a nightmare for dealing with actual songs, even if all songs will have the same tracks (though mine pretty much never do). Also, my albums have generally been a combination of singles I’ve put out since the album prior to that, new songs I’m recording for the album (but which I might put out as singles prior to the album release), and new songs that will only end up on the album, and I’m not going to e ready to make all the relevant album-level decisions at the point of being ready to release individual song singles.
As for your second question, what I have done is individual song projects, as if they were going to be singles, even if they were only going to be included on the album, where the songs can stand alone, be pitched into sync opportunities when applicable, etc., then, when I am ready to put the album (or EP) out collect the individual songs for sequencing, remastering, etc. within WaveLab Pro. WaveLab’s montages allow replacing audio files within an album if, for example, you need to remix a song for the album within Cubase, even while doing the mastering in WaveLab. There are also excellent tools for dealing with things like level balances between tracks, be that pre- or post-mastering chain.
On my most recent album, though ten of the thirteen tracks had previously been released as singles – of the other three, one was a remix, another was a new recording of a song I’d previously released as a single but with a different genre, and the other was a new song – I knew I’d need to make mastering changes from the single versions in working with the album. I could conceivably have done this in the Cubase projects (since all the single releases were mastered in those projects). However, I knew it would be easier to listen to the sequence’s flow if I did the remastering in WaveLab, so I started by going back to the Cubase projects, documenting the mastering chains, and saving lots of presets within the plugins in those mastering chains. Then I took the unmastered mix audio into WaveLab, and recreated the song-by-song mastering chains from the documented plugin order and presets to be able to use as a starting point. Any mastering-level adjustments would be made in WaveLab, but, if I had to remix a song at that stage (and I did for at least one of the songs, maybe a couple), then I’d do that in Cubase and replace the unmastered mix audio in WaveLab.
The only real downside of this approach (besides the initial setup work) was that WaveLab’s user interface is way different from Cubase, so there was a decided learning curve, even on the second project I worked on in WaveLab (the album I was describing above – I’d done a 7-song EP the previous year, but I was mostly using WaveLab for sequencing in that case as I was doing a bunch of remixes in short order in Cubase for the EP, and I could be conscious of areas like sequence and level matching while doing that).
I’m working on another album now, but it will also come out as a bunch of singles over time, and I’m not worrying about things like level matching between singles since I’ll end up remastering those when I’ve got the full album together. The only difference on this one is that I already know what the songs will be up front (except maybe for one or two I may write new to target the album), whereas the most recent album really started as a collection of unrelated songs that I figured out later how to fit into a coherent album.