Nice to see you round' these parts of the internet too! I hope you get many forwards and deals for your music with Taxi. It would be well deserved!
When I write you back, please remember that I am just an aspiring writer and composer, and without the artist background that you have. So you may be a newbie on an Internet forum but you are way more well rounded as an artist. So, this is just another listener opinion.. and Im somewhat biased by having listened to your work (and bring that with me when listening), now at least for a couple of months too, and from the fact that I review from your backyard (in Denmark), so to speak.
To your specific bullits:
Is lyrics OK?
I think this lyric is on the poetic or abstract side to submit for general singer/songwriter listings, but it would have to depend on the particular listing (like everything else with Taxi). As far as I remember this is very much your style, and you are able to put so much emotion and create a vibe with your voice, that it seems natural. This can be a sword of Damocles for you, as your stuff sounds great as an artist, but might not be overly commercial IMO. I belive the poetic qualities can work better for some tv/film submissions (especially epic stuff), allthough I think you'll have a lot better chances if you submit your works as instrumentals, and/or team up with a good lyricist (with english as first language). Another route is of course to be signed as an artist, in which case anything I say doesn't matter if they like you (I might just babble anyway..)

Can this song stand alone with just guitar?
I believe so. I've never heard a song from you that didn't have excellent guitar playing and vere arranged really well. Those skills of yours can hold it's own against anyone IMO.
Should I have someone else singing it?
I think so, but Im biased by recognizing the danish dialect that's in there. I've seen many complementing your voice, and the reality check will is when you start submitting your songs. I would say, though, even if you get good critiques on your voice, test the reception with singers on too. That's the only way you'll really know.
How is the mix?
I think it's excellent! I believe your instrumental skills, your composing and arranging skills and your mixing skills will take you a long way when it comes to forwards and deals. Your weakest side would be lyrics and the dialect in your voice (your singing voice are excellent, though).
I think, and this is just my opinion, you may take things to a whole new level if you team up with a great lyricist and start using pro singers on your work.
justmy2c, Ken