It is a financial advisor trick to tell people that to properly invest, you need dozens of different funds in all different sectors.
If you want simple, easy, and decent returns, index investing is the way to go. And that means you can actually invest in just a few funds. Or even one like your target fund. It really isn't hard, but understanding how index investing works requires one to read and do some basic research, and most folks are too busy, scared, or worried about making mistakes to do their homework.
I just posted the following in another thread, and I think it might be helpful for you as well since it sounds like you're still at the very early stages of figuring out how all this stuff works. I knew nothing up until a few years ago, and found this forum and then Jim Collins and Bogleheads and this is my roadmap for how I got up to speed:
Read Jim Collins' stock series to get a great understanding of how this stuff fits together. Check out his site or get his book (based on the site). It is absolutely one of the best, easy to understand guides I've ever read.
http://jlcollinsnh.com/stock-series/Check out
Bogleheads site for any possible question you could have regarding index investing.
The following are the steps I took:
1. Wrote up an investment policy statement to figure out my goals and plans. This is my blueprint for what goes where, why I do A or B if this or that happens, where I want to go in the future, and how I'm going to get there.
https://www.bogleheads.org/wiki/Investment_policy_statement2. Figured out my asset allocation (AA). This is based off of how much risk/volatility I felt comfortable with and set up my portfolio to reflect my AA (which would also include any real estate).
https://www.bogleheads.org/wiki/Asset_allocation 3. I then took a look at what I held where, sold off everything that didn't match up with my goals in my IPS (I decided I was going to be an index investor holding only 2-4 total mutual funds across my entire portfolio, YMMV). I built a lazy portfolio and I am quite pleased with the ease and elegance of it all (but using a target date fund is basically making a lazy portfolio that charges you only a tiny bit more in expense ratio for them to create a rebalancing glidepath).
https://www.bogleheads.org/wiki/How_to_build_a_lazy_portfolioSo TL/DR: you're fine holding the target date fund across the board. What you need to be asking yourself is does the funds in the target date fund match up with your chosen asset allocation? If so, then you're good. But do think about checking out the links so you understand how this stuff works. It is such an amazing thing to feel completely confident in your path and future and know what to do when.