If you're hosting QNAP at home, you'll need to setup the port forwards to allow outside access and point your domain to it. That might not be allowed by your ISP.
Lemmy is lite on resource usage. For space, it really depends on how much content you sync in, or directly upload. For reference, my own Lemmy instance is using 7.4GB of space after being active for two months.
Free speech is a basic human right. No politics necessary.
It depends on what you mean by safer.
Active cellular devices are location tracked. That information is correlated and sold. There's nothing GraphenOS, or any other on device software can do to stop that.
When you carry a connected cellular device, you're not only reporting your own location, you're being tracked in reference to other people that are also carrying a cellular device. Between the two, it's a detailed map of your lifestyle and people you know or may know.
A land line reduces the tracking to a single location, and the people you communicate with on it. Personally I avoid the land line too unless there's no other good option.
For private communication, there is Jabber (XMPP), Matrix, and other self hosted services that avoid the entire issue.
If you really need communication on the road, then there are a couple of services that provide cellular connectivity without personal information. It's not ideal, but better than nothing.
I'm writing all this from the perspective of the US. Other jurisdictions may be different, but location tracking is ubiquitous as far as I know.
The simplest way is to not own one. Get a land line and an answering machine instead. It's ok to not be reachable every minute of every day.
Personally I think it's a great idea. I run my own instance even though I'm the only user and have no communities.
Pros:
Moderation: Your own moderation capabilities. It's your choice what you see or don't see.
Content longevity: You can do your own backups and don't have to worry about loosing content when another instance disappears.
Performance: Generally speaking you'll have better performance. You won't have to worry about an influx of new users taking the instance down due to overloads.
Cons:
Domain: You need your own domain, which is an ongoing cost.
Hosting: Like the domain, you need to pay for hosting to run Lemmy. You could try running it at home, but I would not recommend it.
Management: Depending on how you setup Lemmy, there will probably be ongoing maintenance work. It might not be worth the hassle when you can just use a third party instance and let them deal with it.
Ultimately it's up to you.