1. Definitely buy the plot of land as soon as possible. Finance it with a variable rate at a good interest and that's it. You really can't go wrong with that. The saved equity can then also be used to cover the incidental construction costs! You might quickly need €50,000, depending on what you are planning! It would be great if you could provide us with some important information here.
2. Please do not include the incidental costs... They should definitely be paid in cash during the interest-only period, from saved equity or something else.
Regarding 1., I can basically only agree. Are there still additional purchase incidental costs? At least notary fees and land transfer tax will also be incurred...
What I do not understand is why the incidental construction costs should be paid from equity. If they are calculated properly, they can simply be included in the overall financing package. In my opinion, this is totally normal.
Which incidental costs do you mean in number 2?
Purchase incidental costs? Construction incidental costs? The furniture?