Amortization is basically an accounting technique for periodically lowering the book value of the loan. To make it clear we need to understand that our monthly payments have 2 parts: interest part cost of the loan, principle the main part. These are calculated monthly with the same interest rate we use, but keep that in mind every month we have less debt as we paid some already. So when you do these calculations monthly and write them down a table of payments, we call it amortization schedule.
The interest part of the amortization is only depend on what you borrowed and the interest rate. It doesn't care about your the loan term. Lets say you borrowed 12000$ with 10% interest. Your cost this month is 100$, assuming you paid 500$ principle: next month remaining loan is 11400$ and its cost will be 95$. You can continue this calculation and prepare your own payment schedule.
As you are able to imagine increasing the loan amount is simply adding additional risk within the long run. However if you don't have any savings and simply applying for a loan, increasing it for 1-2 months just in case can be a better plan. You'll be able to keep them in a saving account as insurance. Again should mention these are completely bound to your conditions, earnings, savings, credits score etc. thus any recommendation given here are entirely personal and suggest you to check all details before apply for a loan.
Another issue is, watch out your due dates and ensure you are able to pay at least the minimum. If you can't pay it or interest rates are too high, you should think about negotiating this together with your bank or even some banks offers loans with lower rates and transfers your debt to theirs, if you'll be able to convince them that you just are on good track.