Is T Tauri a compulsory stage for stellar evolution? Do all stars go from Protostar stage to T Tauri and then to Main Sequence or is T-Tauri stage only for certain stars?  If only certain stars, is that those that are less than 3 solar masses which i see mentioned?  (https://en.wikipedia.org/wiki/T_Tauri_star)
Yes, only certain stars that are less than about 3 solar masses were T Tauri stars. Here are some reference and quotes that I saw to answer this question. There are all review papers.


  Our planetary system was formed in early stages of the suns evolution. What the sun was like at that time can be learned by observing young solar-mass stars. 


https://link.springer.com/article/10.1023/B:ASYS.0000003267.35552.f7


  T Tauri stars are newly formed low-mass stars that have recently become visible in the optical range,


https://www.annualreviews.org/doi/abs/10.1146/annurev.aa.27.090189.002031


  This review presents the main aspects of the body of knowledge on T Tauri variable stars, which are presumed to be young, gravitationally contracting low-mass stars.


http://iopscience.iop.org/article/10.1088/0034-4885/47/2/001