Back to levels : IMO it's a good habit to start mixing at low levels, 2 main reasons being that you want to keep headroom for the final mixing/mastering stage and that many effects plugins are modeled after analog gears, therefore they are waiting for audio input signal around -18 / -20 dBFS ( digital world ). Real world console and analog gears like compressors & such are often based on the vu-meter scale and 0 dB Vu matches -18 / -21 dBFS.
So if I follow your mixing workflow, you started right, then you have to take care that you processed each track following this effect input levels rules. At that stage, we are often tempted to compensate the levels using the effect output gain, but you have to take care to keep your levels in this vu-meter range, this wil help to have a more consistent mix.
The problem here for levels might have been that you processed too much each tracks to compensate the initial low levels and when the tracks sum them all on the mix bus and hit the Ozone 8 preset, ozone limiter & compressor are receiving too much signal and therefore crank up & distort the overall level.
Working with vu-meter, or using K -14 or K -18 metering or the LUFS metering is the solution to take care of those levels and the relative loudness of your track. Not using this generally leads to your ears tricking you ( that's basically what always happen when we start to level up things, it's seems to sound better but it's really not in fact ).
So you want your Mix Bus to have a consistent & well balanced audio "image" of all your tracks but still with a relative low level. You still have dynamics & clarity at this stage and lot's of headroom to hit the mastering chain and the final Ozone limiter.
Very good insights about those levels in this course BTW https://www.sonicacademy.com/courses/loudness-and-metering-with-kirk-degiorgio
About MONO : There's many ways to check out your mix in Mono, some audio cards gives you a dedicated button, many metering and loudness metering plugins offers that too, then you have the visual approach with tools like iZotope Ozone or Insight or Mastering the Mix Levels to name a few.
But again, it all start with taking care of each track and IMO using mid/side EQuing is a good approach and also using frequencies filtering ( for example to prevent some low end to hit a reverb or an effect. So it's like sound sculpting & placement, you control what should remain in mono and what could be spread in stereo with M/S Eq.
A final mastering Eq with high pass & low pass filtering before anything else to get rid of unwanted frequencies as well as a final Mid/Side mastering EQ can also help on the master. Then I can't recommend enough to A/B your mix against reference material to check where you stand. It's trial & errors and probably the most difficult part if you're trying to get a so call "home mastered" track yourself : so easy to ruin a mix at this stage just abusing of a few knobs
About Feedback : There are some mixing/mastering people that offer this service ( paying most of the time ) you have to search for this on the web, just Google this "mix feedback service" and you'll find many results.
Recently some new online applications like "Pibox" https://pibox.com/ became famous and are been used by people like Marc Mozart to offer a mix feedback solution. Being part of audio communities & platforms like "Blend" can also be a way to get some feedback, there's also the collaborating side of things and again new software & platforms following the Pibox approach can help. Tom Frampton ( head off "Mastering The Mix" ) has created "Bounce Boss" to help with collaboration & feedback and he's also offering mixing & mastering services. https://www.masteringthemix.com/blogs/learn/sending-audio-files-with-bounce-boss
Many platforms such as "Landr" are offering Cloud Mixing/Mastering solutions too, is that reliable ?? Some people like that, some do not believe in it at all, but anyway it all start with a good sounding mix by your end before thinking of "virtual" or real human mastering of course. IMO, platforms like Landr can help to balanced or leveled a mix, but they won't make magic like a Mastering engineer of course. Some of them offer digital delivering services too, so it's another thing to take into account.
That's some insights & tendencies according to what's going on in the cloud & internet era but back to the root and taking time to learn & practice and to reference your work against reliable tacks, to A/B as much as you can when using effects and to keep in mind that it takes time & implies frustration, one can get there and achieve very good results in the box and with nowadays high end plugins used accordingly.
And last words are : keep the fun while making music !! That's probably the most important, don't let those frustrating moments take it out from you, there's a time for creativity and to feed & being fed by your muse, and there's a time for the technical part and get it sounding right, don't let the 2nd one kill the essence of it all
Cheers ! ( and sorry for long writing BTW )