I have an iPad 3 also. Still works good, but that generation is a bit slow...I'd love to upgrade, just can't really justify it yet. That being said...
I use mine with WiFi only. Have never used cellular at all. Even traveling, there's usually WiFi at a hotel/motel I'm staying at. Or if I really need it, I can always find it at a coffee shop or other similar place. Or...often the best option once I discovered it...set up a WiFi hotspot on your iPhone. Just activate the Personal Hotspot under Settings on your iPhone.
Not sure though about your charging issue. But if you bite the bullet and get a new iPad, it's likely 32GB will be about the smallest amount you can get.