Bike Reviews

I will be moving to Bristol (UK) and I understand it’s quite hilly so I want a mountain bike and since I won’t have a car, I will use it to transport things around and don’t want to just use a backpack. But I never see baskets on mountain bikes, panniers occasionally. I only see baskets on non-mountain bikes. When I was in Holland, I didn’t see baskets on mountain bikes (though Holland barely has any hills so mountain bikes aren’t necessary). Is it dangerous to put a basket on a mountain bike? Like it interferes with the gears or something? Thanks

I have a fairly cheapish mountain bike, recently I have found that when too much pedal force is excerpted, the chain seems to rise up and off of the front largest pedal gear sprockets.
Do I need to remove a link or two from the bike chain because the chain may have become stretched over time?
Or do I need to adjust the derailleur thus to increase chain tension?