If you plan to contribute to a Roth IRA please lookup the backdoor contribution method given your salary level.

Good questions. The target date funds will provide ample diversification and you have access to really good target date funds. If you want to be more aggressive you can select a target date that is 10 years beyond your actual desired retirement date.

Ideally you want fees that are at 0.10 or lower. I'd recommend not going above 0.50 for any funds.