Yes, for 401k, that is correct. Specifically, if you contribute or your employer contributes (though in most cases employers only contribute if you contribute so it's mostly the same as saying if you contribute).
Yes. But then why are you not contributing more into your 401k? You just have to make up your mind to do your planned pre-tax contributions for each year all to IRAs or all to 401ks.
No. In the case where you are contributing to the 401k (and are thus covered by an employer retirement plan), and I'm assuming you're filing as Married Filing Jointly, your AGI would have to be below $98k to get a full IRA deduction. I think your $184k number is from the case where you're not covered by an employer plan, but your spouse is, and you're filing jointly.
