Premanand Maharaj Ji
Can I do only mental seva of Thakur Ji, or must I do physical seva first?
Start with visible seva before mental seva
Without visible seva, the mind and body do not become pure, and mental seva is very hard to reach. The path is naam jap, Bhagwan's leelas and hands-on seva.
Without doing visible seva, it is very difficult to reach mental seva. Yes, if some perfected saint takes you straight to mental seva, that is a different matter.