we started our marriage on a similar basis, both in school, already big student loans racked up, baby coming right away, bam, bam, bam 3 kids (no insurance) you get the picture. DH is German so he was born frugal, I was born poor so I learned it (certainly not my nature).
First Sunday at our first parish priest gave the $ talk, so DH tithed 10% of take-home from the get-go, we have always done it. if we did stop during lean times, we found each and every time the solution was to start tithing again. the # is not important, the consistency and commitment is. One hour’s wage could be another sound guideline, for example.
The reason it works, in my opinion and experience, is that it puts work and the fruits of work and all material things we have in right relationship with God, and corrects our own attitude about material things and about our work.
advice # 2: cut up the credit cards, if one of you has to travel for work or maintain a work expense acct., keep one card for that purpose and do not use it for anything else except work-related expenses.
buy on lay-away, or just save money in an account for what you need, and reorder your ideas on what you really need vs. what you want. we had to learn the hard way, hope it goes easier with you youngsters.