is my logic about dotted eighth notes and bpm correct?

If you set a metronome to 60 bpm (and assume that a quarter note is a beat), then

to count off eighth notes, you would need to set it at 120 bpm.

I am less sure about dotted eighth notes but am thinking I would need to set it at 80 bpm? Is that correct?

I have a simple delay pedal and I'm trying to figure out how to explore dotted eighth notes. So I am thinking that, using the above example, I will set a metronome to tick off an 80 bpm pattern and then set the delay on my pedal to sync with that. Once my delay is doing a repeat at that interval (i.e., a dotted eighth interval), I would then reset the metronome to 60 bpm and play to that. Does this make sense?

Thanks

Yes, that's correct.

60 / .75 (3/4ths of a measure) = 80

There are also metronomes that will tick the subdivisions within the beat. 

https://theonlinemetronome.com/online-metronome

And eventually you want to work toward being able to count the subdivisions without having to hear them, relying only on the 1/4 note downbeats.

Best of success with it!