last, at last 同lastly 有無分別??

Last= occurring or coming after all others, as in time, order, or place: the last line on a page.
At last=the final thing of all things
Lastly= in conclusion; in the last place; finally.
So they are a bet different to one and other, but you can still use them to end some thing expect for at last. You used first and second for the first two points, so if you use finally than it will be right.

hope it's gonna help you

(1)No differences
(2)No,only at last and lastly
(3)Yes
(4)lastly
(5)No