What about the rivers? How would the lack of oceanic water affect the amount and / or characteristics of the fresh water available on the planet?
Salt water is the product of fresh water dissolving sodium and chloride ions from the ground it flows over and pools on, taking billions of years. Rivers on a world with a hydrologic cycle but significantly less ocean water would still have fresh water rivers and lakes, as long as there is rain and aquifers to filter and store it.
The thing to remember about rivers is that you need precipitation to make them possible. Much smaller oceans means much less moisture in the precipitation cycle; if it rains at all. Unless you can get enough water in the atmosphere as 'clouds' to reach a critical mass, it might not rain at all. You'd probably get (at best) dew on the ground on cold mornings, when the latent humidity reaches dew point.
Dew wouldn't be enough to get rivers to happen as these need sustained rainfall or snow-melts to form. (Snow melts are just another form of delayed precipitation - snow falls and then builds up until it melts to form a stream)
So; rivers and streams would be (at best) rare. Shame really; the rain cycle acts as a form of purification for water, allowing it to be cleaned and returned to the land, eventually forming rivers. Without this, fresh water is unlikely given the sustained mineral absorption of water in the ocean.
See the answer to this related question
It depends what you mean by substantially and where the water is.
Someone has actually posted what the oceans would look like with 95% less water (based on a simulation I believe) in the above question and there are still enormous areas covered by water so almost certainly enough to drive the hydrological cycle.
But most of Earths water is in the Mantle - also see the above question. So it might well be that the above much smaller shallower oceans simply drain away into the mantle to replace some of the water lost from there. It really depends on the exact conditions.