As long as they can collectively dump the BTU load into the space to be heated, you're on the right track.
Ideally, You'd want your return water to be at the temperature of the space being heated right before it re-enters the tank for another round.
Systems usually aren't designed this way, however, because that last radiator will appear to be doing nothing, since it's payload has already been dumped upstream.
For maximum efficiency, you want to move as much
energy as possible, and worry less about the actual temperature of the radiators. So in that case, more radiator surface = better.
Unfortunately, a lot of people equate a higher temperature with a system 'doing more', which simply isn't the case. Heat is heat, and if you're moving all of it, then you're maximizing your potential.
There is of course a such thing as overkill, so there is little point in adding more radiator if your stove isn't putting it out. Somebody else on here is likely to give you a more concrete method of determining where the line is for a given input (ie the math), but of course this can be tricky to tell even with the proper formulas; your heat source is DIY and so you must calculate it's output yourself. There's no spec plate to tell you.
Once you know what your production abilities are, you can get a much closer guess as to what your radiator requirements are. Try to match them as closely as possible (ie BTU input from stove = BTU output from radiators) and your system will be close to ideal.
Then all you will need is a thermostat to control the pump!
Make sense?
Steve
