In the customize UI options you can drag them into a toolbar aswell or hotkey them (category "Poly Tools"). Just saying because I find them incredible usefull ;) You need to be in one of the Editable Poly submodes to activate the floater though.
Vertex snap the last vert to the first vert and then use the straighten loop tool (Graphite) to bring the others in line. Straighen loop is pretty well hidden. you need to go to the ribbon in edge mode. Go to Loops Loop Tools A floater will appear with the loop tools. they rock :D