well i'll tell you this from experience the pda plan will not allow your bb to work right. they accidentally set me up on pda and my messenger would not work nor my emails.so i had to call them and get them to switch me to a bb plan. so stick with the bb plan and as far as tethering are you planning on using it as a modem
Go for the $35 plan, not the other ones. Welcome to CRACKberry by the way. Notice that crack is in upper case letters? There is a reason for it. Have fun and enjoy.