You're unlikely to find any kind of tablet device that has all of those things.
For starters, 4G wireless is just a marketing term that doesn't mean much. Sprint is going the WiMAX route while pretty much everyone else is going the LTE route, but even then they're using different frequency ranges so it's not like they're going to necessarily be compatible. Add to that the fact that none of the major carriers has launched 4G service in more than a small handful of areas, as well as the fact that it will likely be 3-5 years MINIMUM before there's any kind of widespread buildout of 4G service, and it's really a pretty pointless thing to be looking for at the moment.
A full sized USB port would mandate a certain minimum thickness to the device, and the name of the game is thin and light with tablets. The best you might be able to do is MicroUSB to USB.
The ability to print to your old printer would assume that the tablet is running some version of Windows. Most run some version of the Android OS, Apple's runs its own iOS, and of course RIM's PlayBook is running a custom OS that will eventually become the new version of the BlackBerry OS. To date, no tablets run Microsoft Windows of any variety. Maybe once Windows 8 is a bit more ready for prime time, but even then Microsoft is basically saying that there won't be broad compatibility between the different versions. A tablet running Windows 8 on an ARM processor won't be able to run Windows programs from your desktop using an x86 processor. The same would go for drivers to support hardware. The closest any of them have to this, that I'm aware of anyway, is Apple's AirPrint, which I'm not really up on the specifics of, but I believe allows you to print via your computer and a wireless connection. I know a lot of tablet makers are working on NFC which, if you had a NFC ready printer, might work, but if you're planning to use your old laser printer, you're going to be SOL with pretty much any and every tablet out there from now until the end of time.
I know the iPad 2 has a forward facing camera, pretty sure the PlayBook does too, and probably most every other tablet out there.
The decent processor speed will mean less decent battery life or less decent performance. When it comes to processor speed, performance, and battery life, there are only certain combos of two that can be made. Higher speed and performance means shorter battery life. Higher speed and longer battery life means most of those clock cycles aren't really doing much work, so lower performance.
Sounds like you want a laptop still. If you're willing to replace your printer and forget about the 4G nonsense, then a tablet MIGHT work. Assuming you're actually in an area with 4G service, you can always add a 4G cellular modem dongle, though I suspect you'll be sorely disappointed with the results. The signal on those things is notoriously fickle, and will drop out sometimes for like no reason. They work fine for simple things, like web browsing, but if you try and download anything, forget it, most of the time that'll stress things too much and they'll drop the signal. That's all before you contend with the rather stingy data caps, usually in the 5GB/mo range. Cellular companies, and lately regular broadband providers, would much rather impose data caps than actually build out their infrastructure. It's more profitable that way. They can run around advertising all the bandwidth sucking things you can do, like stream music and videos, then charge you exorbitant rates if you actually DO any of those things. Then they can run around overselling access to their service, and blame "a few data hogs" for the fact that their service sucks.
What might work as a good compromise for you is the new MacBook Air model. It's light, easily portable, it has 2 full USB ports, it runs the full Mac OS X, has a Core 2 Duo CPU where most netbooks have an Intel Atom CPU which gives maybe 65-70% the performance clock for clock. The performance will blow your old iBook out of the water, battery life should be pretty close to the same as your iBook in its heyday. The only potential points of concern is that the Air is not upgradeable. It uses a custom form SSD in place of a HDD, and while there are third party options in that form factor, you need a very difficult to find screwdriver to get the bottom case off the new Airs. The RAM is soldered directly to the logic board, so there's no upgrading that without getting a new logic board. So you need to be sure you're getting everything you need at the time of purchase with the Air.
So ... I am currently on my 2003 IBook running 10.4.11 Tiger 1.07 GHz and wanna rejoin the world and become mobile. This is really lagging at everything now.
I have the money to buy a new "something" today. But what is it ? I was looking at a variety of pads and devices but each seems to be lacking a key thing I need.