Payment plan developer - completion and land

We would like to buy an apartment in a residential complex. The payment plan presented to us by the developer is as follows:

[*]30% after the start of the groundworks
[*]28% after the structural shell completion including carpentry work
[*]12.6% after completion of the roof surfaces and gutters and window installation, including glazing
[*]10.5% after completion of the rough installation of heating, sanitary, and electrical systems, interior plaster, excluding patch plaster work
[*]4.9% after completion of the screed and tiling work in the sanitary area
[*]10.5% after completion of the facade work and after readiness for occupancy and simultaneously upon transfer of possession
[*]3.5% after full completion

70.6% after completion of the closed shell (30% + 28% + 12.6%) seems too high to me. Shouldn't the final installment after full completion be at least 5%?

I also have 2 further questions regarding the contract

[*]The developer reserves the right to make changes in the planning and execution method and the intended building materials, “as far as they prove to be technically appropriate or necessary or are based on official requirements.” I am of the opinion that this is not a valid reason. Furthermore, the changes are not sufficiently transparently specified. It is the developer's responsibility to know the building regulations and technical requirements and to take them into account already during planning and pricing.
[*]According to the contract, site access is only possible in individual cases. I assume I can enter the construction site at any time as long as I register in good time, and of course entering the site is at my own risk.

What do you think?

Google "payment plan real estate agent and property developer ordinance" and compare the figures, that matches quite accurately. The 70% includes the land and all planning work.