Like others have stated, you can stay in 3 rivers and take the car or shuttle to Sequoia, otherwise you MUST take 180 in. 198 is signed nothing longer than 21ft, and they are serious. You can stay in the Grants Grove area on 180, or just outside the park at Hume lake.
I am not sure about if there are tunnels on 49, but the Wawona tunnel on the Hwy 41 alignment (not signed as a Hwy inside the park) is just before heading to the valley floor. There is a scary sign with a low clearance number, but that is the clearance at the curb, and the tunnel is arched so just stay near the center. Tour busses use it every day. The viewpoint just exiting the tunnels is famous and spectacular, not to be missed.
Making a loop starting at Coarsgold going to the Yosemite valley, exiting on 120 through Groveland and circling back to Coarsgold would make for a long day of mountain driving and not doing much else. Best would be just return the way you came. If you did want to make a loop, take 140 and come out at Mariposa. While 120 to Groveland is very scenic, it is much like other mountain routes. The valley is really the highlight. If you had the time, instead of making the big loop, you would be better to go 120 East and take in the unique high country and then back the way you came. (Not sure what time of year you are going, high country may be closed)
If you are going after the 1st week in March and like trains, check out the Yosemite Mountain Sugar Pine Railroad just North of Oakhurst. They have 2 operating Shay locomotives, very few of these left in operation.
Enjoy your trip!
2007 Expedition EL 4x4 Tow pkg
1981 Palomino Pony, the PopUp = PUCampin! (Sold)
2006 Pioneer 180CK = (No more PUcampin!):B
Me:B DW:) and the 3 in 3 :E
DD:B 2006, DS ๐ 2007, DD :C 2008