Catho,
Just a suggestion, only buy one of your trips via Tiknet, and then wait to buy the rest of your tickets after you get there (provided you will have internet access, if not, then just buy them all).
The reason is that you have to show up in person and wait in line the first time you buy. The remaining times you buy you can just show up at whatever train station and use the electronic ticket dispensing machine instead. There is never a line for it. Also, I say wait to buy the rest just so you don't have to carry them around and potentially lose them.
Also, if you elect to use the electronic ticket dispensing machine, be sure to use a credit card, and a credit card that you have a PIN for. The machine will ask you for the PIN of the card and you must have it. No way around it. I say credit card, instead of debit, because there is better protection for using credit cards than debit cards.
Tiknet rules. Good luck!