Yes, definitely!
I spent many months making a clone of MapleStory in which it is single player and has more fast-paced gameplay. It was my first project ever in Construct 2, although I did use MMF2 and other software for a few years before I found C2. I spent so much time working on it on my own, using the Scirra forum to ask questions I needed to ask here and there, and came out with this!
I'll upload a video so you can see what I managed to make.
Here is vid:
[TUBE]http://www.youtube.com/watch?v=eRywKLbrF7M&feature=youtu.be[/TUBE]
But anyway, to answer the specific details,
Large-scale sidescroller
Yes, definately, as long as you design the level appropriately (Not one massive 10000x1000 image, but instead, lots of small repeated tiles/scenery.) You should check out Remember not to waste your memory and also take a peek at the Tilemap object for level designing efficiency! (I personally didn't use the Tilemap object, it didn't exist at the time I made the game!)
Character Classes
Yes! Depending on how you plan to implement the logic behind this, this could be a breeze. It would tie in with other things like if you planned to "Only warriors can equip 2H swords", then that would tie in to the inventory logic, where upon attempting to equip something, detect the class that the item allows, and detect the players class, and if they match, then equip. If not, then popup message saying "No" :P
All items could be in one "Family" called "Items", which would allow you to assign Instance Variables to that family, such as "Name", "Description", "Str", "RequiredStr", which will make it super easy to implement things later on like inventory/equip stuff! Making "Class specific" items (like, how to assign the property to items so that they can only be worn by 1 or 2 classes) could be done in several ways but my mind is currently blank on that right now, very tired indeed lol.
Drop tables
Yep :P See, here is where I should probably say "Use Arrays/Dictionaries/XML" or something, but when I made my game, I didn't use anything except pure Construct 2 events. I do recommend you learn about those things if you don't already, I reckon they'll allow you to handle drop tables really well. You can have all the properties you desire, like rare/uncommon (You could do it like Maplestory with the % chance, I think I made the Blue snail shell in the video have 90% chance of dropping or something), you just need to prepare the correct logic to make that sort of system!
You're not in over your heads at all, it's totally possible to do it, I've done what I've done single-handedly, I can imagine you and your friends working together as a group would end up creating something way more cooler (and neater)!
If you have any other questions, I'm more than happy to answer them :)