It's not either/or but "both, and".
Judaism has a system of rules, halacha, by which we are to live our lives. Halacha is not negotiable, so that might sound like "all or nothing". Instead, think of it as what you aspire to, even if it's not what you currently do, which is closer to "do what you can" (but not a free pass :-) ).
As Dan noted, there are conditions where halacha itself provides for prioritization, but this is built into the halachic system, not something that individuals get to decide. If you think your individual circumstances call for a leniency on any matter of halacha, you should consult your rabbi for guidance. Your rabbi is in a position to evaluate the demands of halacha, your financial situation, your family situation, where you currently are in your growth in torah, and so on, and advise you about your job.
When we face barriers to fulfilling the law we should be striving to remove them. In your case, your job currently requires you to work on Shabbat. Can you do anything about that? Can you trade shifts with somebody, even if it means your new shift will be less convenient? Can you find a new job that doesn't have this requirement? If you can make either of those changes, so that you can remain employed and also keep Shabbat, Jewish tradition calls on you to do so. Remove the barrier by changing jobs, rather than saying "there's a barrier and I can't get past it".
I'm not trying to give you personal advice (that's not what Stack Exchange is for) but rather to illustrate an approach. Yes, Judaism has rules, and when you violate them you are sinning. Yes, Judaism has some affordances for sufficiently-severe circumstances (and for this you should consult your rabbi). And yes, Judaism calls on you to take action yourself where you can to improve the situation.
And, all that said, if what you're asking is "if I can't do all of it should I do any of it?", the answer is yes. Every mitzvah you do counts in your merit; it is better to violate Shabbat and still follow other mitzvot than to say "well, if I can't do Shabbat I'll just punt". Doing a mitzvah can lead you to do another; that's a good thing.
(I realize that this answer is lacking in soures.)