Need help Upgrading my trailer electricity

My horse trailer is a 1989 model and some one else did the wiring install and it is really bad and I'm tired of it. I bought it used and didn't know what I was looking on wiring . But now after seeing new installs and reading this forum I've got a better idea what I'm looking at.
I want to go with 50 amp 4 wire number 6 gauge service because I have a 7k onan gen with two 30 amp breakers.
I would like ideas on a manual transfer switch , a service panel and a inlet supply for shore cord. Money is tight as is everyone's but don't want junk either.
I know when I start searching this equipment I want find everything out there .
I know a lot of folks here know what works and what doesn't for the best price . Thanks for reading.