@freegeekss
Welcome to the expat.com forum and good luck with your potential move to Bulgaria!
You're an EU citizen, so you can move to any EU country, for any reason, with minimal red tape.
There are a number of remote workers / digital nomads here who have chosen Bulgaria as their new base. Apart from being a nice country the main draws are low living expenses, low income tax (10% flat rate), and relatively low property costs. Several started in Bansko - the largest mountain/ski resort here - and got a small apartment there as their European base (starting around 25k euros).
Your 130k is an excellent income by most standards, so congratulations on that, keep up the good work! The official minimum salary here is about 350 euros per month. As your net income will be around 30X that... you can see that you can live extremely well here. (Or live well, and save a lot in order to invest in property or additional business ventures.)
Yes, you're correct that it's between being a freelancer and having your own company. Self-employed is probably simpler, and maybe cheaper. But a company is probably the one that an attorney or accountant would suggest. (For a detailed discussion/recommendation, it's probably worth having a bit of an attorney consult. It's easier to have one anyway for your residence and company incorporation.) It's probably a little more flexible if you have multiple clients and you don't spend all your time in Bulgaria. And, as you say, a company has limited liability.
I think you'll find that Bulgaria is not as restrictive about your allowable expenses as many other countries. So while you think you have low expenses, my guess is that you could include all your geek hardware (computers, screens, printers, peripherals, mobile phones) as expenses. Internet, mobile phone contracts maybe. Worker salaries if you use remote workers in India to do some of your grunt work. Even an allowance for a home office (or rental if you prefer to walk to work). International travel if you visit clients and/or work onsite. Company car, private pension, private health insurance, and similar executive benefits. The company option also lets you chose your salary, so you can keep it lower to pay less tax and social security. The balance can be kept in the company as accrued profits, or you can pay some/all of it out as dividends (more tax efficient than bigger salary, usually), or you can buy some property as your office.