When adding an unconnected person in this search box, include also a marriage date event option.
A marriage is a shared fact between the 2 parties. If you have a marriage date, then why use the unconnected person option?
A more common request is to add a field for the Christening data. This, and burial detail, are far more likely to be found in older records than birth and death details.
I sometimes add such names with no added details, as I believe the best place to work from (once the new ID has been created) is from the Details page. From there, you can add whatever vitals information you have available, then add a spouse to the "unconnected" individual, Straight after this you will have the opportunity to add a marriage event.
Once you have filled in as much data you have to hand, it is likely you will be provided with "Possible Duplicate" suggestions, which often show your newly created individual already does exist in Family Tree - the duplicate (once verified as such) will probably have parents, and even siblings, attached. The usual practice is to then keep the older profile (probably will more information / sources than yours) and merge the ID you have created with that.
Obviously, make a search for any sources that relate to the person. But, again, when using the source linker I am reluctant to carry detail across at that point, as it is better to return to the Details page first to verify what might be unreliable data found, say, in a census record.
In summary, at the "Add Unconnected Person" stage you hardly have to enter any detail at all. Any suggestions for an existing, matching profile within Family Tree should soon appear once you get to work on the Details page, from where you can then make any appropriate merges with existing IDs.