Wow! Do you know how to ask some good questions! I'm sure you will get plenty of advice from the knowledgeable ladies here.
I need to get breakfast started so I am only going to post my solutions to all these issues.
I went with a Netbook with extra memory. Most netbooks comes with 1GB of memory but it makes it slow, so I bought a 2 GB sim (about $50) and upgraded it. With that hardware I can now do everything I need to do....and it is fast! I easily put the netbook in my purse and take it with me. I can carry it everywhere in the house one handed. A normal day will have me using the netbook in the kitchen, dining room, bathroom, bedroom and living room.....so you can see it is truly portable.
Firewalls - most netbooks come with Windows 7 starter as the operating system. It is good about setting up your security. I go with its recommendations 99% of the time. When you connect to a wi-fi spot (say your at a book store and want to use their internet service) the software will ask you if this is a Home Network or a Public Network - if you select Public Network then it will configure your firewall settings to protect you from strangers.
I like using the IPad, Nook, etc and am seriously considering buying another one. They are FANTASTIC for their purpose but no keyboard & software I need keeps it from being the main stream pc usage.
Something that might only matter to me.....I love the colors the netbooks come in. I have a hot pink one that is my main netbook and a purple one that is my backup. As you can tell - I love love love my netbooks.