Hey Hugo,
Here are my "don't take this for gospel" answers.
1.1 Don't offer rent credits to the tenant buyer. The seller will be happy with getting their payment covered for the most part, if not work a deal with them.
1.2 They can add anything to the non refundable deposit, just make sure they know it is for option consideration and they lose it if they walk. Also, make sure it is spelled out that any option consideration MAY be credited to the sale price but is in no way a down payment. The only way I would even bring this up is if they were short on what you want as an option deposit. ie... you wanted 15k but they only 12K but will make you whole when they get their tax refund back in a week.
2.1 The renewal deposit is whatever you both agree on. If they miss the option window due to something beyond their control( scores didn't come up as fast as they thought they might, interest rate rose and made their backend ratio too high) and these things can be handled in 6 months or so I wouldn't change them a renewal. If on the other hand they haven't done anything to help their cause and maybe even hurt their chances to cash out, I would think about a big renew fee and/or not renew their lease. This is a judgement call for you to make. At the end of the day your goal is to make sure they get the home if they want it.
2.2 If you cross mention the documents, a Judge will be confused and could treat the non-performing tenant buyer as a tenant only and make you evict them. Or the Judge could treat them as having ownership in the property and then you would have to foreclose on them, and depending on the state you might have to deal with a redemption period, up to one year after the foreclosure where the prop is in a holding pattern. That is except for taxes, which you will be responsible for. It is easier to deal with an eviction, so I advise to remove all doubt.
3.1 Don't give the tenant buyer a copy of the Option agreement
3.3 If you file the option at the courthouse(the one between you and the tenant buyer) it will cloud the title. If things don't work out, you might have to give the tenant buyer some money to release the cloud, if you can find them. They have you over a barrel at this point and could ask for all of the non refundable deposit, plus some. This is also the reason I don't give them a copy of the option agreement, they can record it if they wish. Now, if you are doing a lease option with the seller, they you want the lease and the option to be the same form and you want to record it. This will keep the seller from taking a mortgage out on the property without your knowledge.
Take the above for what it's worth, I'm not an attorney and make claim that the above is 100% factual. That said I've been in the real estate/mortgage industry for a bit.
Holla if you have more questions