if the pattern says that gauge: fine, that is your reference point.
make your swatch. count it out. tell us the result. If you differ from the instructions, let us know how many stitches you have in e.g. the front piece. then we can tell you, by how much your garment will be off and if it needs to be fixed or is fine.
don't stress that much. Things look way more scary in the fog than bright light. Just keep asking and we keep telling.
you want stripes in your hoodie. Good choice, I like it. Team look: great.
but you do not have to change the pattern for making them.
I assume your pattern will tell you how many rows of knitting you need for the front, the back and the sleeves (and the hood) or (more likely) it will tell you for how many inches you will keep going with something.
Well, you just go ahead and substitute one yarn for the other at the beginning of a row. (typically one uses a right side row to start a new color, but that only matters if you do garter stitch). then you work that row, work back in that yarn and: there you go: a stripe of 2 rows tall is done.
If that is all you want: change back to your original color.
If you do a taller stripe, twist the original color yarn and the stripe color yarn once around one another before you work row 3. then you do not have a trailing thread at the side (it is called "cabling up" sometimes).
the same thing you do, if there are more stripes in the other color and they are not soooo far appart (lets say about 6-8 row max). then you cable up the stripe color and use it again when it is time. for longer stretches: cut your yarn, leaving a tail to weave in and start over once it is time for a stripe.
you make your life incredibly more easy if your stripes or the main color always start in a right side row. (meaning they come in even numbers of rows wide). then all your yarn changes happen on the same side of the piece and you do not get confused.
the stripes you can just ignore, though, in the counting of rows or measuring of inches for your pattern. it will still be the same length.
I assume you chose the same type yarn for both colors? then the size will be identical anyways.
if you do stuff like those stripes, pay close attention to the "brand name garment" about where to place the stripes and how to combine them. The eye is very used to that and recognizes differences quickly. the big brands have it figured out well.
I could imagine to do the cast on and 2 rows along each piece in the stripe color (in the ribbing then) to give a professional touch.
also little accessories sometimes really make it. Can you get a sew-on-tag somewhere? A small thing with the team logo? partially a key chain attachment, earring or the like... if you mount that (sew on) somewhere on the piece, that gives a very professional touch. I like that with garments because it takes all prejudice to the right side: "Great piece!" comes first, then "where from". If you don't add anything like that, fine anyways, of course.