1. T-Mobile and Vodafone have the best 3G-coverage, which is almost equal. Congstar is cheap with € 0,35/MB, but several discounters on the eplus-network (Aldi Talk, simyo, blau, solomo) are cheaper as they charge only € 0,24/MB. eplus doesn't provide HSDPA, but only regular 3G with 384 kbit/s, however the lower bandwidth may be helpful to control the costs.
solomo's pro tariff is also very interesting for their cheap international rates: calls to European fixed networks (including Ukraine) cost € 0.09/min and to mobile networks € 0.29/min.
Alternatievly Vodafone and T-Mobile offer 24h-flatrates. With
Vodafone's webessions, which work with every German Vodafone SIM, you'll get unlimited access for 24h for € 4.95. T-Mobile offers the same thing as
web'n'walk dayflat, but their sessions are billed starting at midnight, no matter when you started the session. So Vodafone is the better choice, as you get real 24h.
2.+3. Instead of a PCMCIA card I would recommend a USB-stick, as they're cheaper and because you can use a USB-extension cable to position it e.g. on the window sill when coverage is bad. T-Mobile branded web'n'walk sticks are sold at eBay Germany from € 75:
http://computer.search.ebay.de/web-n...inZtQQsbrsrtZd
Be careful to buy one without SIMlock! Those without SIMlock say "frei für alle Netze" (free for all networks).