You can never get away from the cutting noise, whatever you use (unless you design an enclosure), but a spindle will still be quieter overall as noise from the motor is so much lower. I used to have a Bosch 900 Watt router but switching to a WC spindle made the workshop so much quieter.

Another advantage of a spindle over some routers (the plunge type with the handles out the sides) is the ease of mounting and stiffness of the connection to the Z axis.

If you ever take the plunge (!) and switch to a spindle I promise you will never look back.

I think you can make a very capable machine with supported rail, so don't worry too much about that. I would however recommend looking at used profile rail for the Z axis (£80 = 300mm pair from FA Systems on ebay for example).