Bah, flux works fine. Mig is better, but I understand the train of thought that leads people to start off with a less expensive machine. You've already got the machine - just roll with it and learn.
I don't know that you need a top-of-the-line helmet, but my welds sure benefitted from auto-darkening. I struggle to keep my hands still when I can't see them.
Flux core can be tricky though. What type of materials do you want to weld? There are different approaches depending on the thickness. Autobody sheet metal is totally doable with a flux core welder - but you have to do stacked spot welds in my experience.
I highly recommend watching some youtube videos - no matter how well we might describe it in text, it is probably easier to just see someone do it. Like my welding sheet metal example - I remember the first time I tried I just burned holes in everything even on the lower heat settings. It just didn't occur to me that I should pay attention to the heat I'm putting into the metal and proceed with a series of tacks. Seems obvious now.
Conversely, you might want to crank up the heat and do short tacks if you want to ensure penetration but are fighting not to burn through thin metals. Would you think of that on your own? Maybe, if you're smarter than me.
I like
Lakeside Autobody or
Make it Kustom (the former is awesome for autobody repairs like a collision shop might do (think quick but durable), the latter delves into more complicated metal shaping an fabrication - but there are specific videos the fellow has done on welding techniques with different welders. He also makes fixture, jigs, tools, braces, frames, etc, so it's not just sheet metal welding.