The use of stepped wings is for low performance easy to build planes. The drag tends to be high and the aft part of the wing produces little lift. Hard to get clean effective air flow to the control surfaces. You may end up using large deflections and therefore large drag to get a response
Clark Y is a high lift high drag wing. The use of various airfoils is dependent on the purpose of the plane and the speeds it must fly. I cannot say if the Clark Y is the most suitable. A Clark Y is many airfoils. Most airfoils are defined by a specific cross section at various percentages of thickness.
So an SD 7080 can be built at various thicknesses. These are expressed as a % of chord.
A very thin wing is hard to build strong and can have low drag.. A very thick wing has a lot of drag but it is easier to build a strong wing.
This link http://soartech-aero.com/
has free downloadable technical journals. which are now here
You might want to download and skim to find the relevant areas you need for your plane. The "Airfoils at Low Speed" (SoarTech 8) and the 3 others below it are VERY valuable. You should have a copy of each of them.
Also see the UIUC links given on that page.That is where you can download them. Even if you do not read or skim through them all, download them as serious reference material for the future.
If I recall correctly there is a summary of the types and their application with each various group tested. That will lead you to a possible more suitable airfoil for your plane.
Also for good aerodynamic info go here.
Short informative and technical articles by a leader in aerodynamics.