I assume you mean 4GB space - ie memory on your hard drive? I'm not an expert on iPlayer but my thoughts:
1. If you have downloaded them onto laptop and iPlayer has not a built in time limit to watch them - yes. You say though that you are using a dongle which would suggest that you haven't downloaded anything and want to use the dongle Internet connection to watch them. If so then No, as iPlayer cannot be watched overseas without using a VPN to hide your location - a bit complicated to explain via this text
2. No more than it would in the UK. The laptop may slow down a bit though if it's memory/hard drive is nearly full
3. Open p windows explorer, plug I your memory stick and drag the files from their current location to your memory stick. Again though I did not think the BBC/iPlayer wold allow you to do this