assalaamu alaikum yazdimuslim
even though our beliefs may differ on this in regards to the Mahdi and the Messiah son of Maryam.
We do agree there will be a Mahdi to come, and actual human being. If he is one of the 12 Imams that is hybernating somewhere ready to come out to lead the muslim world after 1300 years ago from his last appearance, no we do not believe this.
I would agree with the Shia madzhab and others that the daabbatu minal-ardh mentioned in the Quran is a human being who will be raised by Allah as a Mutakalim to speak to all mankind for doubting in the signs of Allah. This might very well be the Mahdi to come, but not as the Shia think or any of the various schools of thought think.
History has shown, that everytime a figure was to come each religious group misinterpreted such expectation by 65-85% . I think for us as muslims the mahdi will appear unexpectedly from what we expect.
The Hadeeths have already shed light on the matter that there will be a big commotion about him, meaning he will be doubted and will not be accepted at first until Allah confirms his status.
As for me personally from learning from the past experience of others is to leave some room for anything possible to happen. If he is rightly guided by Allah then he will not favor either Shia, Salafi, Sufi, Sunni etc.
As to the matter of the return of The Messiah Son of Maryam. Keep waiting for him to come back, all of you are going to be in for blue disapointed of a no show until the day of judgement .