If over 75% of the computer usage will be browser related, get the Chromebook/Chromebox.
If iPad typing is an issue, I have this keyboard at work and love it:
K480 Keyboard – Multi-Device – Logitech
Allows to switch between 3 different devices. I have one at the office set up to control my Mac, iPad and Nexus 7 tablet.
Upgrading with SSD is a great idea if you already have the laptop available. There are a plethora of $300-400 laptops out there to choose from as well.