You just copy and paste the link to your site. No site is too small to be eligible, so far as I know, though Delta does have the right to deny (initially or subsequently) participation by anyone they deem not worthwhile.

So far as I know it's fine to purchase your own tickets through your own link. A few retailers now prohibit this (e.g. Amazon), but not Delta.

I've found the Delta affiliate system OK but not great. There are some indications that it's not reliable -- that only some of the purchases made through my link actually result in me getting paid by Delta. On the other hand, the money I receive from the surviving purchases is nonetheless enough to pay my yearly hosting bill, so I guess I have nothing to complain about.

I do use Ebates sometimes, and I get small checks from them occasionally (maybe twice a year, depending on purchase size and frequency). The $1 commission rate on Delta purchases is a little stingy -- Ebates (and I) get $3 from Delta for each successful, tracked sale, and $1 out of $3 is not such a big ratio. Usually Ebates gives users almost the full commission it receives; I don't know why the ratio is so much smaller here than elsewhere. In any event, when using Ebates, I strongly recommend against accepting the "moe money maker" software that they (intensely!) offer. That software will cause Ebates to take commissions from all the sites you visit, at the expense of any affiliates you may have wanted to support. And the way Ebates pushes the software to users (trying to foist it on users every time they log in to Ebates etc.) is in my view misleading.