Going down is very much viable...going up is much more challenging due to range.
The river is navigable from just downriver of Minneapolis to the Gulf.
North of St. Louis the river is controlled by lock and dams and is fairly easy cruising (limited currents to deal with) with plentiful facilities for pleasure boats.
South of St. Louis, the river is free flowing with wing dams that keep the currents high and limit areas to safely anchor
. There are only a couple places for pleasure boats to refuel before the New Orleans
, so you need quite a bit of range. If going down river, the current
helps with range quite. It can certainly be done but can be challenging.
Up river is a much more difficult problem primarily due to fighting the current
and resulting range reduction.
Most folks peal off at the Ohio
River and take the Tennessee River which connects to the Tom Bigbie (Tenn-Tom) and comes out at mobile. Plenty of facilities and dams keep things much more under control.