Delta Rat

I just got a Colt M4 Carbine and I'd like to replace the handguards......I know it's easy to get them off but to to sure about losing the front sights to replace with a free float. I have read that it leaves big holes in the barrel? What if after removal I replace it wit the pins.......in new in this game and ANY help would be huge and appreciated. Also any recommendations on what would fit my rifle? I like the smooth longer type. Justin Also any other upgrade suggestions?