Learning to deal with metric is really no problem. It will become second nature. What seems weird sometimes is American cars because they nowadays have both.
Later, after you have adjusted to things and gotten to know how your bike runs and what to do to keep it running it will be routine and not a mystery at all like so many things are in the beginning. You should appreciate how the bike was built and it may occur to you that it was originally all metric. Many riders have been through this same thing and if not forewarned about this issue they put some SAE fasteners on their bike but later decided that it was a bad move. You may not have a wrench for that SAE fastener. Or if the nut is missing will you remember that a metric one that looks right really isn't.
Those of us who have been around this stuff for a long time can sometimes spot a wrong fastener from 5 feet away. with out even touching it. It just doesn't look right.
It might not be a big issue and certainly you would use what ever is available in an emergency. But trying to stay all metric is really the right move.
Never memorize something you can look up.