There are two ways to handle the marriage record problem. The issue is that most of the databases want to link the marriage to a "marriage fact" that's already in the timeline (a few, if adding a new spouse at the same time, will do it in one step - but that depends on the database).
One thing you can do is to create a "marriage fact" (that is, add a new event) for the earlier marriage, before trying to add the record. The system typically defaults to trying to add the record to the earliest marriage (which in your case, is the one you want so no problem).
If you already have the marriage fact you want and the system is trying to add the record to the wrong event, you can fool it by adding the record to the spouse's profile - just click "add to someone else" and enter the spouse's name. Be warned, however, that a few of the marriage databases will not add the record simultaneously to both spouses - just one of those "amusing" little glitches.
To add a census record to an occupation fact that you already have created, you will need to first attach the census record to the profile. As "occupation" is not an indexed field, you then add the census record to that fact by going to the "facts and sources" tab from the profile, then selecting "source citations." Go down the list to the record you want, and click the link next to the word "detail." On the next page, on the right side, you will see "edit citation" and "delete citation." Click "edit citation," make sure there is something (anything) in the box that says "detail (required)," and then go down to the checkbox list at the bottom of the page and click on the "occupation" fact you want the record to support. Then click "save citation" at the bottom, and you're finished.
This same method works for any citation you want to add manually, when you have a record that supports facts that can't be added automatically.