The beachcaster with the fixed spool will be ideal. Multipliers can't
really be used for float fishing or feathering.

Tackle shops usually sell sea float kits that have the required float /
weight combination - the tricky bit is the stop knot to prevent the
float travelling all the way up your line as the weight sinks. "Power
gum" is a really good rubbery kind of line that can be tied as stop
knots. The stop knot can be hard to get right but a web search or chat
with the tackle shop should sort that out.