Essays / Proposal essay conclusion: "as discussed in this paper" or "previously mentioned" [4]

yes it is possible. It is the best way ever to conclude. a recapitulation is always needed in order to remind your reader of the points evoked in your writing.

Writing Feedback / SPEND Vs SAVE; Most youngsters today are not hesitant to spend their money! [3]

you will soon lack of money. there is something missing in the sentence. it may be better to say you will suffer a lack of money very soon.