The offset is one parameter of wheel design, but in itself has little meaning without knowing the width of the wheel (and tyre).
If the wheel is only 7" wide, an offset of +20mm is probably do-able. But if the wheel is 8.5" wide, ET25 would be too little and the wheels would sit too outboard and the tyres will rub, so it would need to be more like +35mm.
Hence, there's a relationship between the offset and width, as to what will fit the car and look good. A google search will link you to many websites explaining wheel specs; very useful to have at least a basic understanding.
If you have a wheel in mind, ask about it, because people will know if it fits and looks good. Or are you looking at aftermarket wheels?
Stuff like the 17" Supersports look decent, but the offset is relatively high, so they sit 'very inboard' and looks 'bad' IMO. So it's an example of a wheel that fits, but doesn't really suit the car.
As above, you are unlikely to notice a difference in handling unless you drive the car hard and fast. But increased 'track' will confer increased stability, but can adversely affect turn-in/cornering bite.