Hi Swexx
I don't know a lot about singing, which seems to be your primary focus, so perhaps this is useless to you if you don't care much about the mixing. If not, there's simple tweaks that I think would improve your mix.

The music sounds like it was compressed and had its mids cut and bass boosted, which makes me believe you're editing with loud volume and/or headphones. If you're not using a compressor, it is likely that the software you're using has a built in limiter and your tracks are so loud they're triggering the limiter almost constantly, creating that "pumping" sound on the music when the vocals come in.

It is easy to underestimate compression when the volume is high. There's a tiny muscle in your ear that will change its movement according to how intense the sound waves are, to protect your ear from damage. Meaning it will make very loud, continuous sounds seem quieter. This is essentially a natural compressor, and if you're mixing loud you should know that your perception of dynamics is very hindered. My personal preference is mixing on low-moderate volume to listen for any drastic changes in volume or too much limiting.

Cutting mids and boosting bass is a trap. People are sensitive to mids (particularly around 3.4 KHz) and as such mids are very aggressive on the ears. Removing them is an easy way to make the music softer on the ears and allow yourself to push its volume even louder, but you're deleting a lot of information from your song, especially taming the guitars too much. If you google images "phons loudness perception" you should find a graph that shows real sound pressure (dB SPL) for certain percepted loudness (phon), tanking at around 3 or so KHz. It's tough to get stuff at the right level when they have a lot of mids. I like the car test for this, if guitars are a tiny bit too loud in the mix they will almost always blow my ears off in my crappy car system, while all other professionally produced music will sound perfect.

I would personally not touch the low end on an already produced song if I don't have a good listening set up. The Parkway Drive cover you posted sounds very bassy on my very trebly cheap panasonic headphones. I recommend having a reference song on a separate audio track while you're working, if the song is similar to yours there should be no problem trying to match the sound for a start. It seems Mixpad supports VST plugins, in which case you can use something like SPAN for looking at the spectrum of your reference and your track.

I don't know how you got the instrumentals though so they might just have poor sound, in which case there's not much to do.

Delay and reverb in that order can indeed make your vocals fit in the mix better, but use conservatively.

I think you shouldn't really be doing much for mastering for now. If you really want to, you can optimise your audio file for Youtube streaming by using something to measure LUFS and adjusting your track accordingly (seems to be -13 LUFS for Youtube). Here's link about LUFS, here's a freeware plugin that measures LUFS (displayed as "Integrated Loudness"). You do it by applying on the master, resetting the plugin and playing your track all the way to the end, the integrated loudness value should be the LUFS of your track. Plugin is for windows 64bit which I'm assuming you're using.

Hope this was helpful in any measure, good luck.