You should try to to evaluate the negative for contrast and choose a grade before you do test strips. If you aren't sure and have not printed before, than probably start with 2 or something close. If you do the test strips with no filtration and then you dial in a filter, you will need to do new strips, because your times are likely to be way off. Once you have a little more experience, you will start to recognize situations where your neg is flat and needs higher contrast and the opposite, but for now starting in the middle makes sense.

Now, there are two different sets of filtration numbers on the Ilford info sheet. If you use the one with single color filtration, dialing in magenta for higher contrast and yellow for lower, you will totally change the amount of light reaching the paper when you adjust the filters. If you use the second set of values for your contrast, then you will be changing the light values very little when you change grades. Keep in mind, however, that you still will likely need to adjust your exposure some if you change contrast, but it will be much less if you use the second set of numbers.