The trouser length can always be adjusted to the wearer. Similar to the sleeve length. It is important to ensure that the fit around the hips and thighs is correct, since afterwards hardly any changes are possible.
Normally slim fit suits are able to buy in an entire suit. But if You want mix up colors and patterns, we are able to do so, that You buy items, e.g. pants separate. So it will allow You to mix and match various colors & patterns - for a wider wardrobe selection.
The rule of how to properly apply a suit jacket is based on an old rule and is still used today. King Edward VII was the "creator" of this rule.