You have nothing to fear but fear itself.
The camera is fantastic value for money. It's classed as a "beginner's" DSLR because it's lacking fancy features and "only" has 11 AF zones.
(First thing I do with any camera for normal use is change AF to centre only; almost always shoot by aiming at what I want in focus first and getting AF to lock in on it.)
The "Effects" mode and all the effects therein are very gimmicky (childishly so) and just removing that from the dial altogether would already make the camera seem more professional. But who cares! The other thing about the whole beginner vs pro camera thing is that you have to go into the menu to change things that on more expensive cameras are more immediately accessible. But again for astrophotography, for the most part, who cares!
As far as the performance of the sensor goes it's only within a couple of f-stops (2-4x ISO) of some fairly recent pro cameras costing several $1000. It's within about one f-stop / 2x ISO of the Canon 5D Mk II & III in terms of low light performance and noise. At least they're my initial impressions (friend of mine has a 5D Mk II). But maybe on long exposures the thermal noise will get worse with the smaller DX sensor. But still, for <$300 one can't complain. And it's great that you don't need to be so precious about it because it's inexpensive. It's small and light as well.
For the money, you cannot go wrong; in fact you could do a lot worse for a lot more. But you really should be asking these questions
before buying the camera.
If you already have so many lenses then it's a no brainer. Even if you don't the F-mount is probably the most backward compatible mount ever made. There are tonnes of decent old film camera lenses available on the cheap. The DX sensor format is especially kind to lenses designed for 35mm film.