8 whole months is extremely light in the experience dept. 5 years including time in a foreman position would be a much stronger resume. But its your life and you will inadvertently walk into some very expensive mistakes from lack of experience.
The size mower for this state sounds fine a 60 would likely be the better choice. As far as gated lawns go you won't be able to do them at first with out a smaller mower. But a main mower is a far more important tool here than what I would call a secondary mower. We run a 52 with a 36 and a 60 with a 44 but if we had to be down a mower we would always pick a small one. They just can't cover the ground the big ones can. You could do the gated yards with a 21 but your soon see it is less than practical when your use to a 60. Bottom line is you have the ability to pick and choose who you work for and many guys in this are pass on the gated bs. The advantages for doing the gated lawns is few landscapers here compete for it so they are easier to score.