What you are asking for is a tall order. If you live on the ground floor, noise issues are more easily addressed because you don't have to worry about impact noises with the floor. Impact noises are the hardest to control, and they radiate through rigid structures like floor joists rather well.
I have no affiliation with the site, but there are a great number of styles for Wing Chun dummies shown here. Another individual has some video instructions on manufacturing your own. You may decide to draw some inspiration from the different models shown on the first site and some sweat equity and pointers from the second link. That will at the very least deal with the reduced space requirements. You have several mounting options, and as long as the dummy is secure and won't topple over during use that will be good enough.
As to noise absorption, the best ways of dealing with it go against the best ways of mounting the dummy. As I mentioned in the opening paragraph, impact noises are your worst enemy in a condo or apartment environment. If you mount the dummy so that it is fixed (i.e. no rotation), then you have some options to minimize impact noise from the dummy transferring to the walls.
- Use high impact rubber as spacers between the top and bottom of the dummy. One low cost but effective material are the rubber hockey pucks intended for indoor gym use (not the kind intended for ice hockey).
- You will likely have to cut the dummy so that the sticks remain at the right height, but you have room for the sound absorption material.
- Use rubber washers between the metal washers and the mounting surface.
- Don't let the dummy's "foot" come in contact with the ground.
- Mount on an a wall that does not border a neighbor. If you have a wall that connects to the outdoors, that is an ideal mounting surface. If you have a wall that is between you and your neighbor, that will be the last place you want to mount it.
- Wrap the arms with high impact foam. This can affect your training and the feel of the dummy, so use it as a last resort.
Last but not least, all these steps can only minimize the noise made from the dummy. There will be noise. As a good neighbor, you may introduce yourself to your neighbors and let them know your intentions--asking if there are times when it would be best not to train. For example, if your neighbor has to get up at 5:00am, they are likely going to bed at 9:00pm. Training after that time would be rude to them. Some neighbors will be upset by anything above a soft whisper, so you'll have to use judgement with them. But as I also mentioned in the beginning, living on the ground floor allows you to get away with a lot more. You can mount your dummy normally because earth is the world's best sound absorber. Still mount the dummy so it isn't on a bordering wall with your neighbor, but you won't have to go through too many extra steps to sound proof it.
note: I have a background in audio engineering, even though I don't use it as much these days. That's where the information on sound absorption comes from.