Gadget was based off of a stuffed robot of the same name.
Cake was also based off of a plush cake, although it didn't really come with a name. (Creative name, I know...)
Since the Tinkers are basically just smaller versions of Gadget, I'd say they're also technically based off of a plush.
When I was first making Gadget and Stickman, I realized that new characters were appearing too fast. After some thoughts, I decided that there would be a new "season" every 100 comics. I decided that was too much, so I decided to end Season 1 at 25 comics. However, when I made it look like the series had ended, I forgot to remove the "more comics coming soon" text. Oh, well!
The first comic I made about Gadget and Stickman was actually drawn with a pencil and paper. Here's a scan of it:
This was slightly changed to become Comic No. 3 in the first season of Gadget and Stickman. It's a bit hard to read because of my poor handwriting, but here's what it's supposed to say:
Interesting, huh?