A few thoughts - no guarantees as I know extremely little about your office...
Gigabit Ethernet should be sufficient for the near future (next 5 to 10 years). It's hard to imagine this not being the case given the relatively slow progression of high speed Internet connections in most places. You'll be looking for Cat5e (not anything else).
Side note for those who think they know about Ethernet cabling categories: Cat3 will do 10Mbps. Cat5 = 100Mb. Cat5e = 1Gb. Cat6a = 10Gb. Cat7a = 40Gb (and 100Gb at short distance). There's no reason to use Cat4, Cat6, or Cat7 as cheaper cables are just as fast.
Make sure they use a patch panel. It's a little extra cost, but saves a world of headache in organization, reconfiguration, and basically any time there's a modicum of change.
The core of the network is the switch, you'll want something managed, but seeing as you only have about two dozen endpoints you'll want to stick to the lower end of that spectrum. The quick and dirty requirement is that the switch has a "console" port (this will be a physical connection as pictured below). I highly recommend Cisco, ProCurve, Juniper, or Extreme (though others are acceptable compromises when budget demands).
Having a managed switch enable a wide variety of possible upgrades, configurations, and utility in solving odd problems. I'd suggest something like the ProCurve 2510-48G; ProCurve gear comes with a transferable lifetime warranty and software upgrades, and it's generally easy to find on secondary source markets (eBay) at very cheap prices. (Full disclosure: I have no interest/affiliation with HP/ProCurve, just a fan of their products).
As for switch quantity and location; I your office seems small enough that you could get away with a single 48 Port switch (a typical office needs about twice as many Switch Ports as there are employees, for printers, servers, and other odd devices that get plugged in). each port on a Gigabit Ethernet switch is capable of 1Gbps in both directions. The switch itself has a backplane capacity, called the switching fabric. If all 48 Ports want to talk to someone else at their full 2Gbps then the switching fabric has to be able to get all those connections to their destinations. Within a modern switch this is no problem.
If instead you get two 24 Port switches, you still have 48 Ports total, but the two switches have to be connected to each other. If you use a single Port on each to connect them, then you have two halves of the network and a 2Gbps bottleneck in-between. There are switches with 10Gb (or rarely 40Gb) connections that can reduce the effects of the bottleneck; but they cost more, and the cable to connect them costs more. You can also bond multiple cables between the two switches, if you used two cables you could get 4Gb total. Which also adds redundancy. Say you only use one cable, if it gets damaged (kicked, unplugged, "oops", etc) then half of your network becomes disconnected. If you're using two cables then both would need to be damaged. And you can generally add up to four if you want. Using two switches is simpler in some ways, especially for the installer. But it does have drawbacks, and the solutions to those are complicated.
You mentioned two APs already; which sounds roughly correct for a smaller office. If your environment is "clean" (no other wireless networks or sources of noise around), or if you're willing to accept "less than great performance" then consumer SOHO gear works. If you want reliable performance and problem mitigation then you should be looking at the same manufacturers listed above (there are other good names out there, prices will be similar). Make sure it's 802.11n, 5GHz, and at least 2SS (dual Spacial Stream; or more is better).
You don't mention what router you're using now. If it working well for you and can handle at least the 20Mb connection you're upgrading to, then it should be good enough at least for the time being.
If you're looking to change; same companies as listed above generally. But, it's really hard to argue against a Cisco ASA 5505, or similar Cisco router.
Make sure everything is reasonable labeled. The wall jacks should be labeled with the patch panel somehow (even if it's just a "map" that shows Patch Panel Port 1 goes to 'this desk'). Extremely complete documentation is going to drive up the price, and a small business isn't like to use it often... But minimal labeling or mapping shouldn't cost extra and allows troubleshooting to be significantly easier in the even of problems.
The above is really all a network of your size is going to need for an optimal Google Apps experience; or any cloud based solution for that matter. The technical guidance Google provides applies almost exclusively to large networks with problems you'll not encounter in small networks.
If you want to upgrade to an IP based phone system in the near future (VoIP) be sure to mention that as it may affect the choice of equipment for some of the above. VoIP systems are a somewhat expensive investment however, it would certainly be a lot to do all at once.