Tykenn,
Yes the saw is a skilsaw, like 10 or so years old with an abrasive blade(s).  You probably can't see but the cord is spliced together in 2 places, when I first got it I was building my deck and accidently cut the cord with the decking twice, lucky I didn't 'cute myself.  It cuts really well and some cuts I used a bit of angle iron to get straight as an arrow cuts.  I was cutting square tubing today, both 90 and 45 degree and started with my dewalt compound mitre saw (not the right tool) and quickly switched to the ole skilsaw.  It is awesome for cutting, at least compared to the other tools I have.  I was browsing through Home Depot today looking at circular saws but see no reason to replace it.
The firebox is 1/4" and I had no problem, I cut about 12 - 14 linear feet on a single blade, only had to change it when I when cutting the square tubing.  Good luck with it.  This is my first project with anything like this and the advice from the folks here and tons of youtube videos (careful some are horrible) plus a little of luck has made this project successful so far and a ton of fun.
Joe