Two penneth from me, jack plane and a smoothing plane, the extra width of the 1/2 types is useful. Wooden versions are also available, and just as functional as the metal ones.
Before you spend all your money on just the planes though, remember that
1. a couple of extra blades are useful.
2. a honing guide and a wider double sided diamond stone to keep those planes sharp is also a must. Leaving them dull will ruin your enjoyment, make the work harder and is generally a bad thing. Plus virtually every reasonably priced plane will need fettling before you get any serious work done.
Colin, Czech Rep.