First answer, yes, if you mix a male with a female and they pair up, you will end up with a tank full of convict cichlids, they are easy spawners and good parents. You will also end up with the pair and their fry taking over most of the tank, defending their 2/3 of the tank fiercely against anything else. Silver dollars, if small, would stand no chance against that kind of attack... and lg silver dollars would likely suffer physical scars from it. Tiger barbs would be convict food early on. Convicts can be great if you have a large enough tank to provide them with suitable tank mates of similar size and aggression, such as jack dempseys, green terrors, jaguar cichlids, etc. Mind you, this would not be a healthy mix in a 100 gallon tank. Once these fish start to mature to full size, 100 gallons is going to be way too small for even 1 of each of what I listed.
So are they a good starter fish... they can be under the right circumstances. Unless you have an outlet for the fry ahead of time, don't mix male/female. The fry grow quick and it can be hard to even give them away for free. You can expect at least 50 - 100+ fry each spawn. Thats a lot of large, aggressive fish who will pair among themselves as they mature.