I am glad your husband is aware of the situation and isn't showing a problem with it. That might change into the future though, so it is something to be aware of.

As far as how to actually start an online d/s relationship? Same with any. Communication. Talk to each other, find out each other's tastes. Let things flow naturally, don't try to force things.

It also wouldn't hurt to set some ground rules for the two of you. From things like when you can spend time together and guidelines for how to handle conflict to any things you may require of him as your submissive.

Just like any relationship (bdsm or not) it takes communication to be successful.

Good luck.