1080i is Interlaced video and 1080p is Progressive Scan video, a better quality image. Very few camcorders will have the 1080p ability. Follow this link for a little more information about 1080p:
http://en.wikipedia.org/wiki/1080p

This would depend on your computer. Some have a Firewire (IEEE 1394 or iLink) connection. It also depends on if your camcorder uses USB or Firewire. If you can please post a little more information:
Brand and Model of Laptop.
Brand and Model of Camcorder.

What you want to do with your finale footage could influence which camcorder would be best for you. If you want to edit the footage the Hard Drive based camcorder would be easier. DvD based camcorders would be better if you just want to record your footage and just play it back. Record time is a factor too. The DvD camcorders have a shorter record time, then you have to replace the DvD with a blank DvD to continue shooting. The Hard Drive camcorders will shot for hours, depending on the size of the hard drive. Whenever you are ready you can transfer the footage to your computer or stand alone recorder, erase the hard drive and shot more footage.

It is always Better to have more storage. Even if you don't think you need it. That 10 gig difference could mean several hours of video. If the cost is nominal than it is worth investing.