The assumption of 3F-force what it looks like now and how much it costs.

I finally decided to invest in two additional phases to my home, i.e. the so-called strength. The situation for me is that the building was once divided into three owners. There is a connection from a pole to the building, then to an "ancient" box with three fuses and then the phases spread around the building, each with its own meter and one phase. I am going to buy myself a welder and a wood cutter and I need three phases. I would like to ask you how to deal with all this with ZE. What are the costs and who pays the costs for what (box, meter, etc.)? What can you do yourself and what does a licensed electrician need?

You mean weave?

The operating limit is determined by the EV at the terminals at the top of the building (as long as it is an overhead connection). Relative to the protection in the connector. Everything that is abroad is owned by the recipient (or the administrator in a multi-family building - WLZ to the main switchboard). Any work outside the boundary of operation of the power plant is the responsibility of the recipient. The description shows that the building already has a 3-phase power supply. It only remains to adapt the receiving installation in the apartment to a 3-phase power supply (cable from the switching station to the apartment, or replacement or extension of the installation) and a new contract with the power supply for a 3-phase meter. Of course, the exchange of measuring systems.
You need to submit an application for the definition of the TWP (Technical Connection Conditions). It is very likely that the EV will wish to take the measurement systems outside (if they are now in the apartment) to a place that is generally accessible in the stairwell or to the exterior wall of the building.
Costs in line with the operator's current tariff. Approx. 138 / kW for cable connection, 110 / kW for overhead. And, of course, the cost of an electrician who will prepare the installation for the new power conditions. A box or a new switchboard.
Greetings.

Of course, the cost of the box, security and cables to the operating limit is also on your side. When I was doing the connection recently, the material closed at PLN 900 but it depends on many many factors.

So I have to call ZE first and inform them about my intention, or should I just hire an electrician and he will arrange everything with ZE? The meter will probably have to be placed on the outside wall, what else should be in this box next to the meter - some fuses and other protections and is it a matter of electrician and my requirements?

Nothing on your own. You are going to ZE. You tell them how much power you need. They give you Technical conditions. There will be everything described, what box, what security. If you have TN-C you will have to split the PEN conductor into PE and N. You give the conditions to the electrician and he does the rest. When it is ready, you call them and they come to connect you to the new connection. I don't know when you sign the contract, but probably at the same time when you will receive the conditions.