Yes, it's all in the rendering rules. BUT: I do not recommend trying to recreate for Garmins the same map style as that of OSM web maps. Something that looks good (and visible) on a large 32bit color monitor will not necessarily look good on a small Garmin screen. Also, OSM web map has way too much content which you don't really have a need for on a handheld unit.
My suggestion is to create a map for your needs (hiking, cycling, car navigation) which only contains the important stuff. If you're not satisfied with the existing rendering rules, copy them and adjust your copy to what you want to see.
Maperitive currently doesn't do tiles, but this will be implemented in the near future. And everything is/will be scriptable, so you'll be able to run it from the command line.
But if I understand correctly you don't really need a tile service, you only need a bitmap generator. Maperitive already does that (it can even generate georeferencing sidecar files like KML, OziExplorer MAP and world file): http://maperitive.net/docs/manual/Comma … itmap.html
The only thing is that you can only work on OSM files and they need to be loaded into memory as a whole, so there's a limit of how large an area you can cover. The maximum I was able to work with on my machine was 70 MB .osm.bz2 file.
No, it's not working currently. Here's an explanation why and a workaround: http://igorbrejc.net/kosmoshome/comment … ment-44842