Congrats bro... nice choice. good thing u got the navigation too. its worth the price.
well, about ur queries... here u go
1) the suspension is definately hard. its tuned more for stability then comfort. the car feels sporty on this setup. theres not much u can do to here. just get some very nice n soft tires, that will certainly improve things marginally. get yohohama aspec A300. they are VERY soft!
2) i like the idea! i had a picture of similarly done seatcovers but i cant seem to find it now
3) YES! it will void the warranty. i dont think Honda guys wud fit it for u. however, do check it from them. they usually offer aftermarket parts installation without voiding the warranty. do check from a well reputed honda showroom.