1. Not sure what you mean by this question. 72c is the IRS provision for equal periodic payments. If at some point before you are 59.5 years old, you decide you want to draw (earnings) from this account (contributions from a Roth can be drawn without penalty after a certain time and with some rules), then you would do so under the 72c rules. There are a few calculators that describe the various assumptions for these withdrawals.
2. The vanguard target dates mostly consist of three funds (total U.S. stock market, total international stock market, and total bond) with different weightings. You most likely chose this because it is a simple option, and if simplicity is what you are looking for, then yes, you should continue to contribute to this fund. As you learn more about asset classes, seek more diversification, and potentially better returns/less volatility, you would potentially want to add more asset classes to your portfolios with different weights. e.g REITs, emerging markets, small cap etc. Also, as your balances grow, you can lower your underlying expense from .18 to ~.05 by simply buying the Admiral shares versions of each fund (Total Stock, Total International Stock, and Total Bond).
3. Not necessarily. Understand what your long terms goals and risk tolerance are. Focus either on dollar cost averaging or value averaging. Vanguard will do the re-balancing for you as long as you're in the target date fund, but you if you go a different route, re-balance every year or so to ensure your asset allocations are where you want to be.
Best advice i can give is to grab a copy of the Intelligent Asset Allocator from your local library. It's a bit technical, but explains the concepts very well.
