Yeah, I used to get to Champion 1 at the start, but people have way more powerful decks now and renting cards can boost a good deck to the top tiers.

Do you know of where I might find a good strategy guide or youtuber who has good builds and what to do?

I don't, and rarely see any strategy posts - playing and watching and seeing why you lost is how i've learnt to do ok.

The thing I'm worried about is do Ineed to level up my summoners to level 3 so i can use level 4 commons and level 2 rares in battles to get into gold or not? Is it possible to reach Gold III with just level 1s?

Summoners are pretty key to advancing up the ranks imo. I don't play at that level so couldn't give you an answer there. What I do know is that it's hard for me to get out of Gold 1 at the start of each season - it is really competitive at this level!

On an unrelated note, Iam kicking myself hard for a few mistakes Imade. I accidentally listed some level 2s and 3s of Alpha cards for Level 1 prices... I accidentally made a big mistake by selling a Flesh Golem level 4 for 45 USD and a level 1 goes for that, so i lost like 350 USD:(

That is a shame :( I know someone who would have liked that Gold Golem, he has 1/3 supply of the non-Gold Golems!

Last year I sold a Gold Magnor for 40 GBP ($55 ish).

Oops!