1) Yes, you can keep your private PRSA and continue to contribute to it while also contributing to an employer-provided occupational pension. I am currently doing this. Main advantage is that I can adjust my AVC contributions easily if financial situation changes. It's also with LA Brokers so low commission charges. Disadvantage is that I have to claim tax back.
2) Yes, you can transfer your entire PRSA into your employer-provided occupational pension. In a previous job, my employer didn't provide an occupational pension. They just contributed to the employee's PRSA. But in order to get the employer contributions, you had to use the PRSA and broker that the employer specified. And that PRSA had the outrageous 5% contribution charge. As soon as I moved to a new job, I transferred that entire PRSA into my new employer's occupational pension scheme. It's a standard process.