I did that commute (Lotus Hill to Ming Chuan Uni) for four years. There are several options, and they all take about an hour. More in rush hours.
community bus to Donghu, R2 or 287 to Grand Hotel (American Club Taipei really), 10 min walk or $70 cab or very infrequent bus (R3, 646, 902, one other i forget). Or continue to Yuanshan MRT and get the MRT one stop. On the way back do get the MRT, else no seats on R2. Also rare 646 direct Donghu to Jiantan.
make friends with someone in LongShanLin, the community opposite, or try and sneak in. 5 min walk to R2/287/646 as above.
community bus to city hall, then mrt via taipei.
community bus to songshan, train to taipei, then mrt. often quicker than 3 in rush hours
new mrt won’t help much: via zhongxiao fuxing and taipei is a really long way round, and getting off at dazhi would leave you with only the rare buses mentioned in 1.
hope this helps, pm for more info