Yamnotri is more of a pilgrimage rather than a trek. i’d visited it in ’97. at that time the nearest bus/car head was at hanuman chati which is around 13km from the actual place.
from hanuman chati the walking starts. the other alternative is donkey (local people may call them horse) or duli (carried by people). the journey is quite challenging for a common tourist particularly a through citybred one.
there are resting places allmost throughout the length of the journey. two of them are quite prominent ’chati’s. we covered the bothway journey in one day walking but that may be quite difficult for most people.
the place has a beauty of its own kind. not everybody may like it. as far as natural beauty is concerned, gangotri/kedarnath/badrinath are better. but if someone is interetsed in covering all these 4 dhams or is actually interested in doing something outvof the way then only should one go for it.
local cheap hotels are available. but I would suggest to have your place booked with gmvn, particularly if you are going in the peak tourist season.
if any one needs more specific info, you are welcome - please write to me.