Mixing the sound of different clips inside or outside FCPX

Hello everyone. How are you doing?
Well, I'm about to finish my first 'official' video in FCPX, and the first video of my life in any software, and I don't know how to deal with the sound. 

I'll explain myself. I come from music, and so I am used to DAWs. I want to set my audio levels at -1.5db peak and -16Lufs because that's what's recommended for a YouTube video. 
The thing is that I have my voice, a piece of classical music with sound FX from another clip, my sound FX with my own 'soundtrack'. What I'd do is taking all out to Logic, I'd mix it there and then, I'd set the level with RX from Izotope. 

I'm sure that it can be done this way, but, is there any way of doing this inside Final Cut? Should mix, then create a compound clip, and then, apply a limiter to that compound clip?

Adjusting the output level visually doesn't look accurate especially when one's a newy. And anyway, I just would like to learn how things are properly done.

Thanks so much!
All the best,

Oscar

P.s: I'm sorry for the lengthy reading

Yes, you you can go to Logic and then import that mixed file back into FCP. If you want to mix in FCP, then assign different Audio Roles to voice, music, and SFX. Compound the timeline and then expand the audio and show audio lanes. Here you can mix and add effects to the individual roles, which are acting like track stacks in Logic. At the top level of the compound, apply the Limiter, much like you would to the stereo out bus in Logic. Remember that if you have to step back into the compound to make any changes, you won't hear this audio work applied, until you step back out.

Here's an article I wrote a while back about how audio works in FCP:
fcp.co/final-cut-pro/tutorials/2446-is-your-audio-mix-too-loud

Thanks so much, Oliver. Believe or not I started reading your article last night and I've just finished it. And now, I log in and I find the writer here.. Brilliant!
It's my intention to follow the process you describe. I have to learn a few things that I'd never heard of but with the guidance of your article there won't be a problem. Well, and if there's something that I can't work out I'll get back here.

Thanks so much once more
All the best,

Oscar

Glad it was helpful, although a lot of that article deals with mixing for broadcast loudness levels. If you do a search for "audio" or "mixing" on this site, quite a lot of articles and tutorials will pop up.

If you do want to mix in Logic, then export an FCPXML from your timeline (project). Import that into Logic and mix. Bounce the mix out, import that file back into FCP, and connect it to your timeline. This works well, although some things aren't recognized, like any speed changes made to audio clips in FCP.

Here's an interesting video that might be useful, since you said you come from a music background:
vimeo.com/423864605

Thanks again Oliver. I've just watch the video and it's been great.
I have to explore this site further. There are lots of things that I'm missing out.

Thanks Oliver. I very much appreciate your help.
All the best

Personally, I much prefer working with various audio clips in either Cubase or Logic Pro than adjusting them in FCPX.

Thanks for sharing, Frank.
So, what you do is get all the clips into a Cubase/Logic project and then bounce and import the stereo into FCPX. Is that correct?

Thanks!

Oscar

Yes, that's basically it, Oscar. As you've read, it's not the only way of working, but it is MY preferred way. There are pros and cons to both approaches of course, and sometimes you will find you must work in FCP. But when possible, I still feel that, overall, you'll get better results more easily doing the main audio editing in Logic or Cubase, and then adjusting length, volume etc. as needed in FCP.  Cheers!

Thanks again, Frank. Thanks a lot. It's always very important to know that something can be done in different ways and still getting a professional result is possible.
I need time to try out both ways: inside and outside of FCPX. After reading you, I believe I'm going for the outside option for my first video as I'm 'in a bit of a hurry.'
I'll want to explore some of the things that I read in Oliver's article, but it can wait a bit.

Cheers Frank!