Is this grammatically correct?

Sentence sounds awkward, especially without context but it is grammatical. Maybe add a comma after thank you since your thanking whomever is distinct from your excitement over starting this job.

If you want your sentence to flow nicer, I'd make thank you its own sentence and add a qualifying adverb to clarify the distinction between your starting a job and working with another employee.

Thank you. I am looking forward to starting and also to working with you.

That's my stylistic preference but there are many ways you could change it to make it flow better. hope this was helpful .

I like your preference.

Thank you. That's nice of you to say.

I like your suggestion, but I unfortunately went with my original one first. I hope it isn't too awkward?