Zenogantner

Does having formal Sensei - Sempei - Kohei relationships attract more students?

No. Because most prospective students visiting your dojo will think you're nuts.
Most people won't understand why you take a social concept from Japan and try to implement it in a Western setting.
IMHO, they are right with their scepticism ;-)

The way you approach training and relationships inside your group is perfectly normal, so don't change it.

I don't call my teacher 'sensei'
Just like you, I call him by his first name.
Everything else would be weird ...

Regards, Zeno