All variants have advantages and disadvantages. And there are various pitfalls lurking!
Since the current total equity (50,000) is not sufficient, the land purchase (68,000 + incidentals) must be financed. The lower the loan, the higher the loan interest rate will be, or there will hardly be any bank willing to finance the loan. For many banks, the minimum loan amount is 50,000 euros.
A longer fixed interest period for land financing is very dangerous. When the remaining financing is due in 2 years, this can only be done with the same bank due to the order of priority in the land register. You will have saved yourself a lot of work ;-) and can only sign the loan contract with the bank that also financed the land. That would be a one hundred percent gag. The only solution can be to choose a variable loan or a loan with a one- or two-year fixed interest period. When the house construction begins, you are free again and not tied down.
When building a house, it makes sense to hold back liquidity. It is very unpleasant and stressful when you need money for a baseboard and have to go to the bank to ask them to please pay out a few hundred euros again. As a builder, you have no patience for such games. If more equity is saved up in the next two years, that could be the liquidity reserve; otherwise, I recommend holding some back from the current equity.
It would be important to now design a financing concept and set up a complete financing plan. And then choose the financier who is suitable for the entire project. That saves, for example, costs for the mortgage registration in the future. In doing so, one should definitely explain one's own thoughts to the financier. That way, they know that they have to make an effort again in two years and that you have an option to finance everything with another financier as well.