Practical tips:
Use an old bike or disguise a new one
Pay attention to choosing the best campground - rural over urban, small over large
Make friends with your neighbour(s)
Choose pitch with security in mind (if possible)
A lock or two, around the frame and something solid
In as awkward a place as possible
In as dark a place as possible
Use bungee cords in and around the wheels/spokes impossible to remove without distinctive noise.
Use a brake lock (can be a simple as a hairband around the brake)
Leave the bike in as difficult a gear as possible.
Having said all that, I rarely follow any of that!
I think it's helpful to take a "whole" view, a holistic approach, if you will. You could use a tent that uses the frame of the bike, but then you can't use the bike!
You could store the bike under the tent, but wait until you need to pee in the middle of the night!
You could load up with locks and alarms, but that will probably mean leaving things at home that will make the tour more comfortable or enjoyable.
Sitting at home thinking about a tour can be positive..... And it can be negative - thinking about all the things that can go wrong.
Bike theft happens, but very rarely in the touring world, especially in campgrounds. Personally, I'd have more anxiety leaving my bike in a dedicated room in a hotel when locals know what's in there and who knows who has access.
I don't know if you've camped before, but in a tent, at night, the noise can drive people crazy! It's the one time I regret having a pretty active imagination!
It's far better to have a calm mind and not be thinking about hoardes of bike thieves lining up!
If travelling solo, a bigger issue is shopping/eating or visiting touristy places if that's your thing (And that's not particularly big either).
The fact of the matter is that people are generally good and helpful. It's probably sexist to say, but in my (male) experience females generally have more assistance offered. Asking in the campground for help or assistance, or simply voicing fears will often open up a whole list of new possibilities.
Bike touring is a wonderful experience. Apart from the travelling, the fresh air, the sights, the independence, it reminds us that "other" people are more like us than we might think.
Nothing wrong with anticipating problems, but I'd suggest you apply the appropriate weight to them.
And, oh, there's a search function you can use to see previous discussions