I have had several tabs, two Android and now an iPad2. As you found the iPad does not have any USB connectivity, a major pain...but that is Apple.
Some android tabs have full sized USB ports
, some do not. Some of the full sized ports
do function in host mode, some do not. It is completely variable across the board. And then....if you wanted to use a 3G cell dongle, you would need a tab that could support that function.
You might check the new Archos G9 tabs that are coming out later this month. I hasten to note...I never actually liked Archos and do not have any connection to the company, but their new line has some very interesting specs, including a claim that they will allow the use of a 3G dongle.
There are actually quite a number of new high end tabs out now from a lot of mainstream computer firms. Most are $500. You should be able to look at them in stores and then google
info online about using a 3G dongle.
Now, all this said, ever though I like tabs a lot, but they are not as useful as a full computer running Win7 (or an apple OS). A netbook that you could buy for under $300 would be more useful and would be able to use all the same drivers that a full sized notebook computer uses, since they use the Win 7 OS. You will find it easier to find and install navigation software
etc. Batt time is close to 10 hrs on most of them.
I use a combination of two laptops, an Android phone
and an iPad2 to work online. Need all of those because I am very mobile and need to be connected full time.
Hope this helps