Congrats on the first prints and a fairly painless startup.

On the clicking, one suggestion is to use a short length of garden hose or similar tubing as a listening aid to help locate the source. I know I had a very annoying click that seemed to be coming from the area of the guidler bearing and hobbed bolt area. I was never really able to pinpoint it, but eventual replacement of every component involved seemed to solve it. A couple of others have reported a similar clicking from that area. I've even wondered if it was simply the sound of the hobbed bolt cutting or creasing into the filament.

Another possibility is the extruder motor is skipping when attempting to do retractions. Assuming your gcode includes retractions, they're not happening based on the rotation of the large gear in your video. Looking through the gcode file in a viewer like gcode.ws will help you understand what the printer is being told to do, including whether or not retractions should be occurring when the nozzle makes a non-printing move from one location to another, as it likely would on infill. Colin's firmware baseline used to set the extruder maximum feedrate (the fourth term in configuration.h DEFAULT_MAX_FEEDRATE) to 22mm/sec. At least two of us determined the extruder motor can't be driven that fast, and that something in the range of 10mm/sec to 15mm/sec is more appropriate. If the extruder motor is driven too fast on a retraction, it'll just twitch a bit without movement each time a retraction is attempted.

The steps per unit for X, Y and Z are fixed by the hardware design and the microstepping selections for the stepper motor driver boards. You can work through an understanding of how the settings are determined through something like Prusa's on-line calculators. Changing the settings based on a fixed size test print will likely create a printer that can only print that dimension correctly, with all other dimensions off by some scaled error. What was the LCD displaying as a print height on the last layer? What does a viewer like gcode.ws show as the height of the last layer?

Jumping into early prints with 100% infill is gutsy. If the extruder steps per mm aren't right, 100% infill won't turn out very well. For example, if there's a bit of over-extrusion, the excess filament has no-where to go and you'll be left with ratty walls and a bad top of the print. The sticky on calibration might be a place to start. Simply listed as another source, Triffid Hunter has a calibration guide that touches on extruder calibration and the countless other things involved in bringing up a printer from scratch.