Hello,
I have never played any Ultima game before and I'm wondering if it would be fine to begin at Ultima 7? Will I not understand the story without playing the previous games in the series?

I would actually at least try to play 4-6 first. If they're too... old for you - fine, but be sure to read a recap of the events in Britannia.
1-3 can be safely neglected though. Be warned that U7 is by far the most complex game of the series. To get into it U6 would be a good preparation, but that one builds on the events of U4 and 5... So at least reading up on them would be good.

This. I think it's the best possible introduction to the series and the older games (which, try as I might, are pretty much unplayable now I think for someone who didn't play them back in the day). Here's the playlist. Unfortunately some of the videos as they are now have some sound issues, some audio has been replaced or cut entirely because of copyright claims. Still, it's a minor issue with a great retrospective.

in my opinion, ultima 5 and ultima 7 were the series high points. i have a soft spot for 8 despite the h8.

Agreed. And both UUs are great games in their own right too.

Yes. Ultima 7 is a good point to start. There is lots of lore around that will form a picture of the previous world through dialogues and books. You'll be fine and it is an awesome game! The two parts of Ultima 7 are the peak of the Ultima series.

After that you can play Ultima 6 - and then Ultima 5 - Lazarus. That one is real close to Ultima 7 in perfection.

Thanks guys :)

Us old farts started with 1. :)

Ultima VII is the only one you should play