Firstly, welcome to the City/Isles/Praetoria! Thanks for playing too.
Secondly, let me just compliment you on picking a MANLY FRONT LINES Scrapper instead of a GO KILL THEM FOR ME Mastermind. (Wink wink nudge nudge.)
Alright, so soloing an Archvillain isn't impossible with a Scrapper...just pretty damn tough, no matter what your build is. Archvillains and Giant Monsters are generally designed to be fought by multiple people at once, but I like your enthusiasm. Scrappers are the solo machine though, you've got that right.
Level quickly with minimal investment? Wat. Everyone levels up the same way, you do missions, you kill some guys, wam bam! You talk to a trainer and now you can shoot three fireballs instead of one. Enhancements, DO, SO, IO etc. are a different story. But at first, you won't have too much to worry about in that department.
An arcane knight seems more suited to Broadsword/Shield defense if you ask me though, but it's your call there. SD and WP are both amazing sets, and you can't go wrong with either one. WP is a bit more well rounded while SD offers some team defense, but again, up to you. And even if SD got nerfed it'd still be pretty great!
Tanks are for tanking, Scrappers are for kicking *** without dying a terrible, terrible death, (I'm looking at you Blaster) if you want to be an "Secondary" tank, then WP/SD are pretty good for that. No need to take Confront either! Who needs to taunt when you can hit someone with a Broadsword? As for DPS, you hit the nail on the head, Scrappers are great at killing quickly (Or moderately fast in some cases). Firey Melee doesn't fit the Arcane Knight all that well, given that Firey Sword only comes into play in a few powers.
Overall, you seem to know what you're doing quite honestly. You did some research, read around a bit, and asked for a bit of advice. My main is a Broadsword/Regen and I have to say he's great.