Hi Yoav,
AndreaMosaic already has the option to create very very big mosaics, and you can split them in any amount of tiles, so that they can be printed one by one. Please try the beta version 3.23 and in the More Options activate [x] Split Mosaic. When you create the mosaic you will be asked on how to split it.
The free version allows to create a mosaic made of a total of 200 Megapixels. This is not enough for a big wall but you can see if you like the software and it's output.
The professional version allows actually up to 2 Gigapixels, so you can create a mosaic of 15x10 feet at 300 pixels per inch (very high resolution) splitted in any amount of pieces you need. If you lower the resolution a little bit, to 200 pixels per inch you will get for example 23x15 feet. But if you need a much bigger mosaic then I can help you too. Just let me know.
Please read the
FAQ for more details about this choice

byeee
Andrea