I have live recordings of my band, I converted mp4 to mp3 and would like to edit out background noise like the crowd, and bring the musical element more to the forefront. I am new to the site, and have only used Audacity to slow down and speed up tracks. Since the mp3 file is only one single track am I going to have issues?
Sorry, That’s going to be impossible. 
Sometimes you can use noise reduction to filter-out a little background “tape hiss” or something like that, and sometimes you can filter-out some low-level AC hum. But, the frequency content of crowd noise (or someone talking, or a dog barking) has a wide frequency range that overlaps the frequency range of the music and it can’t be isolated.
As a general rule, you need to get closer to the stage than the audience. What sounds good to the audience in the room rarely sounds good when recorded. It’s easier to subconsciously ignore the noise when it’s “natural” and when it comes from all directions. When it’s played-back, the noise always sounds worse through the speakers. And, the “room sound” (reverberation) that sounds good in a big room is usually too much reverb in a recording, so you usually need more “direct” sound to override the reverb.
Pros still record in soundproof studios with good equipment and good mic positioning. Pro live recordings are multi-track recorded with a mic very-close to every instrument/amp/vocal, usually with several mics on the drums. There are separate mics to pick-up the audience which can be mixed-in as desired.
Sometimes you can record the output from the PA mixer, but in small venues the drums and amplified instruments don’t go through the PA system, or if they do the PA mix doesn’t represent what you’re hearing (with much of the sound coming directly from the stage).
You may be able to set-up a couple of mics close to the stage, and with another small mixer, mix those mics with the output from the PA mixer’s. Or, you can get a multitrack interface and record maybe 4-channels, or however many you want. (It’s not easy to get a good recording mix with a 2nd mixer unless you can get enough acoustic isolation so you can hear what’s being mixed/recorded without hearing the sound in the room.)
In a stadium show, everything is coming through the PA and you can record a good mix out of the PA mixer. But since those shows are big productions, they have the money & equipment to multi-track if they want to record the show.
Since the mp3 file is only one single track am I going to have issues?
Not an issue.
I converted mp4 to mp3
Another topic - Bad move! 
As you may know, MP4 and MP3 are lossy compression. It’s best to avoid lossy formats until the very end where you might want to distribute in a particular compressed format. Or, minimize the number of times you compress to a lossy format.
Ideally, you should record and edit in WAV. But if you’re using a video recorder, you don’t have a choice. And, if you want/need MP3 as your final format, you may not have a choice there either.
When you convert to another lossy format (MP3) you are going through another lossy compression step, potentially getting more quality loss.
When you open a compressed file in Audacity (or any “normal” audio editor) the file is de-compressed. There’s no harm in that, because the “damage” happens during compression (not during decompression). However, If you export in the same format (or another lossy format) you are going through another lossy compression step.