the product I'm consider to use is an engineering wood floor: 7 1/2'' width(wide plank),5/8 thickness,but it only come with 3 1/2 feet long,it is a click and glueless floating floor over concrete,now I'm kind of concern about the length of the product,because it's not that long, will it be stable,will it cause me problems later like buckling etc...thank in advance for the advice,by the way I'm planning to do this for almost the whole house.

Is it Universal Versastrip? If so, I installed 1200 ft. of it last summer for a guy who needed an inexpensive floor. It was fine and turned out better than we expected. It's not Kahrs but you get what you pay for.