Water has the highest specific heat of all substances. Large oceans collect huge ammounts of heat slowly during the day and release such heat slowly during the night. When the sun is shining above a portion of the planet, the seas absorb a lot of heat decreasing the overall temperature when compared to a planet with a bare rocky surface. During the night, when the sun is not shining, that sea releases such heat to the atmosphere, creating wind. Effectively, seas damp temperature differences. But, for large seas on earth, this effect is limited to the mass of land immediately close to the seas. This is called continentality.Land far away from the sea registers bigger temperature differences between day and night, winter and summer etc, we say that lands away from the sea have a greater continentality, so they are subject to greater temperature gradients etc.
If you spread the water as various smalls bodies of water, you effectively decrease all of the planet surface's continentality, all land will be close to water, so the water will effect the temperature of the entire landmass of the planet. No land will be too far away from water to have a large temperature swing. But, as a side effect, the smaller masses of water will have a smaller capacity to store heat, so the effect of the oceans on the temperature - the capacity of the oceans to damp temperature changes - will be smaller.
Regarding the rugged terrain, montains have the effect of forcing winds to climb. If such wind spend time over a mass of water, it will be carrying water vapour, its humidity will be bigger than normal wind. So, if this wind is forced to climb the mountain range, you will have an area with almost constant heavy rains. Hot and humidy wind that is forced to climb loses temperature, and consequently capacity to carry water. The water falls as rain and the air loses humidity. Upon crossing a mountain range the wind becomes cold and dry. Valleys between the sea and the mountain ranges will be very humid, with lavish vegetation and ecosystem. Valleys after the mountain ranges will be cold deserts, unless they are big enough - and positioned near the equator, to re-heat the wind, a situation where they will become hot deserts due to lack of water.
The planet will not be very windy, because wind is the result of air masses being heated by surfaces that are exposed to sun, the larger those surfaces, the more mass of air is moved as the air heats and expands. If the valleys are completely blocked by mountain ranges, wind has nowhere to go execpt upwards. This will create thermals. If the valley has access to water (its not a dry valley), water vapour will climb with such thermals and create cumulus-nimbus clouds. This kind of clouds are able to generate thunderstorms, heavy rain, blizzards etc. As your sea is small, there will be low capacity to form thyphoons and cyclones. Metereologic patterns will be small, divided in sectors by the huge mountains. Expect a lot of deserts everywhere the land is blocked access to water masses due to mountains.
There will be a lot of mountains with cold tops, forming a lot of ice. If the planet experiences big temperature swings, the ice will tend to melt and form rivers. Rivers will have a big difference between their summer time flow and their winter time flow. Valleys will tend to suffer floods. Rivers will have furious streams. Erosion will be quick due to rivers. Expect to have big canyons over several million years. This can create seasonal rivers. Deserts are more prone to this.
The source of water for the planet will have an effect on water distribution. A bit of water comes from vulcanism. Water trapped inside the planet exits the crust via vulcanism, so if you have distributed mountain ranges, you have distributed water. But, usually, the major source of water for a planet are the comets and asteroids that are rich in water and hit the planet. Planets in young solar systems suffer bombardments of asteroids. This - if we dont consider other variables - allows a random distribution of water over surfaces. This means that the mountain ranges will divide portions of water across the globe. Each valley will have its share of water, effectively creating microclimates. If a valley was unlucky on its share of asteroid/meteors carrying water, and the mountain ranges are trully tall enough to block water/wind passage, such valley will become sterile. On the other hand, valleys with a lot of water will become quite humid, as oasis.
Well, its hard to say, climate is very complex, but those are good rules of thumb to allow you to create a fictional climate for your world setting.
Expect heavy rains in the mountain ranges facing bodies of water and arid climates in valleys blocked from the sea.