Arduino as digital logbook

Hi!
I'm trying to build a digital logbook (for geocaching) using an Arduino Uno (ATMega238p), with an SD card, Nokia 5110 LCD or an 1602 LCD and a PS2 Keyboard.

The idea is that when you power up the arduino, the LCD says Please enter your name:
after the person have entered their name, they hit enter, and a new message will appear: Please enter the date:
I know that I can use a DS1307 or any RTC for the exact date, but that's not important.
After the person have entered the date and pressed enter, they will get the last message: Personal message:
Here they can enter their own message etc. (max 80 characters or so).
All this information will be stored in a TXT file on a SD card.

I've sucessfully printed text to .txt files on sd-cards with my Arduino, and I can also create and delete files. so the SD-card-part is OK.
I've also used the PS2 library in other projects, and I'm used to the 5110 library/LiquidCrystal.h.
I know this is a big project, but I think the big challenge is to store the ASCII characters to something before they goes into the log file. And how do you "backspace" characters if you wrote wrong, and the characters isn't saved at the SD-card?
Can someone guide me through that part? Is there possible to use the EEPROM memory?

Thanks for any help!
(example-log as attachment)

SD card library: SD - Arduino Reference
Nokia 5110 library: Electronics - Henning Karlsen
PS2 Keyboard library: PS2Keyboard Library, Connect a keyboard for user input

logbook_example.txt (137 Bytes)