As regards your post #3 (i.e. easy way for subscriptions), adding RSS feature to Jot would be such an easy way -- everybody would be able to subscribe/unsubscribe without registration. Unfortunately, I have not enough time to deal with this issue. But I can help you with #4.
In order to show IP that the comment was submitted from, you need to insert into your comment’s template [+comment.secip+] placeholder that will reveal entire number. Masking two last digits might be regarded as beginner’s exercise in regular expressions:
<?php
/*
MaskIP Snippet - hides two last digits of IP
Written by http://setpro.net.pl/
Parameters:
ip -> self-explained
mask -> character to hide a single digit (default: '*')
*/
$mask = isset($mask) ? $mask : '*';
return isset($ip) && preg_match('/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/', $ip) ? preg_replace('/(\d)(\.)?(\d)$/', $mask . '$2' . $mask, $ip) : '';
?>
So, finally you need to insert into your template this:
[[MaskIP? &ip=`[+comment.secip+]`]]
Good luck.