All of that's negotiable. It's totally up to the buyer and seller. Incidentally, you've listed yourself as a "Home Buyer," but the questions you're posing sound as if you're the seller. Still, it doesn't matter.
As for interest rate, often the rate charged is slightly higher than the going interest rate for mortgages. That's because the buyer often is getting a benefit he/she wouldn't have been able to otherwise. Example: If the going mortgage rate is 5%--but the buyer isn't able to qualify for a mortgage--then the buyer probably ought to pay more than 5%. That might be 6%, 8%, or more.
As far as the payoff period, that really depends on a couple of things. From the seller's perspective, over what time does he/she want all of his/her money? And from the buyer's perspective, what is an affordable monthly payment? Of course a land contract can also be structured as a balloon payment--for example, payments calculated as if they were a 30 year mortgage, but with a requirement that the remainder be paid (the "balloon") at the end of 5 (or 7 or 10) years.
As for qualifying for tax credits, check with an accountant.
How is the deposit determined? It's all negotiable. It's whatever the buyer and seller agree to. It could be quite small--$2,000 or $3,000, for instance. It could be the equivalent of a 20% down mortgage, so in this case that'd be $16,000.
Really, there are no set rules. I can't say: 8%, 30 year amortization with a 5 year balloon, $4,000 down. It's whatever the two parties want. Obviously, the buyer would prefer to have a lower interest rate and less down. The seller would want to have a higher interest rate and more down.
Hope that helps.