The 6" f/5 can often be found cheap and without a mount, but if you are beginning, absolutely find some secondhand dobson before going DIY.
Or better : attend a few nights at a nearby astronomy club, that will allow you to get a feel of the practice, what you can see, what you should expect...
Depending on your location (city? middle of nowhere?) and willingness to drive to darker skies some types of instruments and targets are better than others.
This kind of kit is focused on being compact and lightweight, but that can be an advantage or a non-goal depending on what you want to do.