Ramanujacharya did spread Vishistadvaita philosophy across India. Also, he wrote commentaries to Brahma sutras based on Vishistadvaita. Before Ramanujacharya, acharyas like Nathamuni and Yamunacharya have authored several important works on Vishistadvaita. Some of the works of Yamunacharya are
Agama pramanya, proving the validity of pancharatra agama
Yes, he is correct because a king, who does not come from a Kshatriya family, is considered as degraded in the scriptures. So, a Brahmin becoming a king is not approved by the Dharma sastras.
See the following:
Manu Smriti 4.84. Let him not accept presents from a king who is not descended from the Kshatriya race, nor from butchers, oil-manufacturers, and
Broadly Ramanuja's school of Vedanta identifies two traditions:
a tradition of personal education including spritual initiation, and
a tradition of Vedantic exegesis.
The most important pre-Ramanujan Acharyas in the tradition of personal education are Nammazhvar, Nathamuni and Yamunacharya. Thir works are well known:
Nathamuni's works are lost but some ...