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As per the situation described in your question the first condition is permissible given that the only payment you make at the end of the day is equal to the 30 percent and nothing more. This 30 percent is considered a loan for you in order to finish paying off for your purchase. And a loan is only paid for what its actual amount is, anything more than the loan which is paid while returning is considered interest.

Your second question is also similar where you have mentioned that after paying off the 70 percent for the rest of the 30 percent the seller is going to charge you 1600 dollars out of which he is only going to count 800 towards the remaining loan and the rest towards rent and other expenses, and this process will go on for 5 years. Obviously this is considered interest as he is charging more than what the actual amount of loan is. 

However it will be considered permissible if at the time of the purchase, this gets decided and agreed upon that you will only own the part of the house which you pay for (i.e. 70 percent) and the seller is going to still own the rest (i.e. 30 percent), then the normal value of the rent is agreed upon and the buyer pays 30 percent of the rent to the seller, and then the buyer also makes payments towards the remaining 30 percent loan. If in a few months the buyer pays off half of the remaining 30 percent then the amount of rent will also be decreased accordingly and the buyer’s ownership of the actual house will also increase by 15 percent. Similarly the buyer will pay off the rest of the 15 percent and become complete owner of the house and will not be liable to pay any rent after that. During this time the liability for property tax and insurance amount will also be divided accordingly between the buyer and the seller. This is considered partnership in form of Ijara. The utilities will be paid by the buyer who is getting benefited from them.        

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