Adding vocals to a recording questions?

Hello all, I hope this is the right forum to post these question in.  
 
I wanted to ask about techniques on recording lead vocals specifically and adding them to a song. 
 
I'm no singer, but I try from time to time just to finish my songs. 
 
I was wondering how some of you add you lead vocals to a song that just requires one vocal? And of course will ask what if it needs more? 
 
The obvious answer I am sure will be : "Well I record it in my daw?".  But what I am getting at is does anyone here mixdown their  music and export it and then re-import it back in to a new project setup specifically for adding vocals only with the music already tweaked and mixed down? 
 
I haven't tried this yet, but I was thinking about doing that and was wondering if that would be a good idea or not? 
 
Positives would be you could zero in on the vocals, but I guess the negatives would be that you wouldn't have control over conflicting volume levels perhaps? 
 
I HAVE ZERO IDEA AT ALL HERE, So I am asking more or less, would it be a good idea for certain songs to create more or less a Karaoke version of your song and re-import it into a new project and then add vocals that way? 
 
I am no pro musician, and no mix master or nothing like that. But I thought this would be a good subject to talk about for those interested because I am interested in the concept and idea. 
 
I mean, why not create a perfect musical mix and export it with the best sound and then re-import it back into your daw and then add vocals rather than having the vocals fight for space in the grand scheme of things where the world of sound goes? 
 
Thoughts? Idea's?  I'm asking because I am thinking about trying this with my next few tunes rather than fighting along with the daw and worrying about how loud I am compared to other things in the song. 
 
Either way. I'd like to know from those of you who are pro's what your thoughts are on this idea and technique and also I would like to say one last thing : "Isn't it all ONE TRACK AT A TIME ANYWAY" if you are a solo artist and how would what I am talking about be any different? 
 
I guess what I am asking is for somebody that is a solo home recording artist that plays it all on their songs, is this a good idea? 
 
Bobby
 

Agree, I track vocals in the project, whether it is a single vocal or multiple parts.  Each part gets its own track.  Sometimes I will record guide tracks with a keyboard for harmonies that I can sing along to.  This could also work for the lead if you are  not a reasonable good singer.

Ok, so I did precisely what you're asking about, albeit because I had little choice after losing my DAW in a robbery and only had the music mixed down to a wave on a CD.  
 
And it will never sound right.  I can tell from listening the vocals were recorded apart from the music.  It just didn't "blend" like it does when mixing vocals like any other track right along with the rest of the tracks. 
 
Now, technically, I suspect it's because the music track's compression and mix down treatment is independent of the new vocal track which isn't sync'd with its processing dynamics.  Or maybe it's something else...I don't know.  But it's noticeable, to me.  
 
I would not do it by design.  Just my two cents.   

Sure, you can do that. Lots of people do.
 
For example, you might be involved in a collaboration with others, where you're tasked with adding the vocal to a more-or-less finished mix. Another common scenario is mixing to stems, where a mastering engineer is given two to four submixes, with the vocals being their own stem. You might want to add your own vocal to a karaoke mix.
 
I myself sometimes finish the instrumental portion and mix it down to a bus even before recording any vocals. It's not my preferred method, but sometimes I'm waiting for inspiration to write song lyrics or for a vocalist to come by. 
 
So yeh, you can do that, and you won't be blazing a new trail in doing so. There are caveats, however.
 
Remember that a mix is the sum of many components working together, each reinforcing some parts but staying out of the way of others. The vocal may be the main focus of a song, but it's still just one piece of the jigsaw puzzle that has to play nice with all the other pieces. That's really hard to achieve when you're assembling a puzzle consisting of just two pieces: the complete instrument mix and the vocal track(s). There will always bit an oil and water kind of effect, where the vocal seems to float on the mix and not be part of it.
 
(VLV: you have my sympathy, man. I thought I was the only one. After my burglary all I had was MP3s.)