At the beginng you should tell us in which country the solo trip will be? There are a lot methods to organize transportation. https://goracemamuski.pl/
It'll be easier to help if you can be a bit more specific with the location in Uttarakhand. If its in the Kumaon region, get in touch with this contact (eco-hunters - 9818082844). This guy has a couple of properties in Mukteshwar and more across Uttarakhand and Himachal.
Go for 3 star hotels as they are located very near to the ports 4 Star hotels are far and travelling back to the port again and again take alot of commuting time
Buses are not that often, Best way is to hire a Jeep for Sightseeings. nd for seeing many Beautiful places You can't rely on Buses as thwy might not be accessible too
It depends on several factor. In every tourist place you will get accommodation as per your budget (except the offbeat places). SO you can choose your accommodation accordingly. So randomly it cannot be chosen.
You can also consider Teaching English as a Foreign Language if you are proficient in English. Teaching while traveling can give you adequate pocket money while also getting free boarding and lodging and lots of local authentic experiences
When do you intend to go on the EBC? Also, what other treks have you done before? Last but not the least, what preps are you taking for the EBC, since it it not a beginner's trek.