Quote:
but do not know which one to get first.
Do you spend time trying to flatten or remove twist from wobbly stock on a powered jointer?
Have you built a planer sled to shim stock and run through the power planer?
Do you occasionally have stock edges that are a little wonky off the table saw?
Do you occasionally have stock that has a bump in the middle that want to quickly remove?
A Jack (#5) plane will help with this. Plane down the high corners until you have a reasonably flat side, then run through the powered planer.
It can also be used to joint and edge flat if the stock is fairly short.
It can also be used to flatten the face of stock.
Do you have a sanding schedule that you are comfortable with?
Or do you loath sanding up through all those grits to get to a surface that is ready for finish?
A smoothing (#4) plane will help with this. It will quickly remove all machining marks and make the surface glassy smooth, ready for finish.
Do you relieve the edges of projects so that machined corner is not so sharp?
Do you often need to trim the end-grain of a piece to fit properly?
Do you need to flush up a corner of a box that isn't quite level?
A block plane will do this.
In fact an argument could be made that those three planes are all you need to do the coarse, medium and fine work in furniture building.