My paternal uncle (Father’s younger brother) had attained the divine feet of Acharya; what are the karmic duties that I have to follow? Am I allowed to worship at kshetrams and hilly Divya Desam? Can I celebrate festivals and render service to Perumal?

After the demise of your paternal uncle, you would have performed kuzhi tharpanam, and observed theetu which is sufficient.
Only the karta should not visit kshetrams, take a holy dip in the sacred waters, and should not visit hilly Divya Desam for a year; and it is not for others.
You can celebrate festivals in a low-key manner since whatever we do, we do it for the sake of Perumal hence we have to celebrate it simply (ordinary manner).