Definitely solid trousers; patterned trousers are very difficult to get right and almost always go with a solid jacket (which, if you are just beginning, should probably be a standard blue blazer if you go that direction). I would probably never wear patterned trousers with a jacket, but again, I'm a bit conservative. I'd wear them with a jumper/sweater or something like that, though.
There isn't a ton of consensus on the board (and I disagree with some of it), but the most relevant is that mid-grey trousers in flannel (for colder weather) and fresco (for warmer weather) go with just about any jacket. Personally, I have no issues with worsted grey trousers for shoulder seasons (some here do not think worsted grey trousers are good) and I also have some wool-mohair blends for summer. To be honest, if you're buying off the rack (and depending on where you live), it may be hard to find flannel or (especially) fresco trousers, but worsted wool ones should be around in most stores.
For that jacket, I think a lighter grey trouser could work, but I'd be more tempted by a mid-blue to provide more contrast. With sports jackets, you want to make sure there is sufficient contrast between the jacket and the trousers. If you have other sports jackets and this will be a look you go for more often, you'll want to have more trousers.