It will be terribly difficult to cycle without a filter (beneficial bacteria can live in the gravel as well - however you would need a LOT...of gravel...and I do mean a lot).
Yes, it is possible to overcondition water, however I'm not sure of the consequences. I've only been going on "since when has over-dosing been good?" I don't use that brand, so I'm very unsure. I use Seachem Prime - the smallest size uses drops, so it's much more manageable.