My wife and I were married for 5 years before we really started to get to the point where you are. You are on a good start, but you are right, it is easy to screw it up. It sounds like your wife is receptive to domination and obedience training should come easy for you if she is taking orders for things that she normally does not do.

Perhaps try pushing her a little bit harder in areas that she already enjoys or is readily complient in and let the other areas go for now, ie., the blow job training (sucking dick when/where/how, etc), position training for display and sexual service, service modes, dress codes, etc, etc. One of the first things that I did to start was to control my slave wifes alcohol consumption (she did not have a drinking problem, I just picked that to start with). She is not allowed to drink anything without my permission and without my mixing it for her (for mixed drinks), even as guests to dinners, etc., she waits on me to allow her to drink. There was only a couple of times right away where she felt uncomfortable in a social setting and she broke the rule.

Punishments initially should probably not be physical (whips, canes, etc.). Maybe a slap on the ass. Try denying her orgasm for 2-3 days while you fuck her brains out, enjoying yourself thouroghly. That will give her something to look forward to at the end of the punishment and it will reinforce that you are in control. Control every orgasm and make her ask for permission to cum. Or punish her with a position or sexual act that she does not normally do or does not enjoy but does because you enjoy it (anal, oral, masturbating in front of you).

There are tons of things that you can do to start finding her limits. Instead of tying her up and spanking her, tye her down and make her cum. She will most likely enjoy this very much and it will get her used to the ropes, etc. Any kind of restraint is initially a bit scary for most folks, go easy on them for now. After a while, if you do it right, you could get her to the place where she feels safe and secure in your bondage. That may take a while.