To get the promos I'm not sure if you need a new Samsung account, which you can easily do since, I assume, your husband already has his setup or you can also get the credit with his account on a new device. In any case, you will get the Samsung credit for that account (but you can't 'share' the credit or add it to the other's account) and a code to redeem the Google Play account. This is where it gets 'fun'.
1) Since you get a code for the Google Play credit, you can add said code to any account, be it your husband's or your own. Whichever you choose, you should still create a new Google account for your tablet, it just makes things better to manage (or if you already have one, use that when setting up the tablet for the first time).
2) You can still 'share' apps between devices, so the apps your husband already purchased can be installed in your device if you add his account to your tablet or viceversa, your apps being available on his if you add your account to his device. Your 'main' account remains untouched, this will just be added as an 'extra' account and you can choose to sync nothing but apps.
3) In the case of Samsung Apps or Movies or Books purchased through the Samsung Hub, the same applies. You can't 'share' credit or purchased apps but if you add the two accounts to the same device or use the same account in both devices, you can.