A job offer is not a job.
Get your feet wet and make sure you're going to stay before doing anything stupid.
This. You don't get paid until you accept the offer and actually start working. Get your feet wet and get the lay of the land. Whether or not it seems like you'll stay there for a bit, start saving an emergency fund. Include all mandatory debt such a loans, credit card payment, bills (car insurance, cell phone, etc...), utilities, rent, etc... how much to save varies by opinion but go for 6+ months. Never touch this money and keep it liquid/accessible....meaning a savings account, money market, etc... at a dismal interest rate. You can cycle portions of it thru short term CD's to eak out a tiny bit more interest. Be sure to add more to your fund if your overall bills and such increase (eg car payment).
Depending on how much you make, the loan type (eg Federal), and what your student loan interest rate is, worry about that debt last. If you make below a certain amount, you can deduct the interest on your taxes. If you were to lose your job, the debt is deferred. In the mean time, making timely payments helps your credit. If you have credit card debt, start paying that down. If you have other debt, prioritize what you wish to pay off (eg smallest first vs interest rate, etc).
Re: 135i, realize that BMW, like Audi and MB, require more periodic maintenance; a lot of which you can do yourself fairly easily. Most people don't pay attention to that and pay for it in the long run. Join a forum and learn about whatever you look at (new or used and regardless of brand). BMW obviously costs more but you don't pay anything for service (parts or labor) for the majority of regular service and repair so some of the upfront markup really is covering that in advance. If you want a newer car, get a certified pre-owned vehicle and let someone else take the initial depreciation hit.
Regardless, start putting something away for investments/retirement now. If your company matches, at least max that out and increase your contribution as your salary increases and debt decreases. If you cannot take advantage of every cent you company matches, at least put into for what they will 100%.