Tactics when buying a kitchen / how to negotiate properly?

My daughter has the "wood" from LEICHT, the wood was also installed by the LEICHT studio, the built-in refrigerator and built-in freezer as well as the front on the dishwasher were installed.

She bought the handles elsewhere, the LEICHT fitter also installed them.

The appliances were purchased separately from a dealer, 2 devices were bought online, an electrician installed them. The only upper cabinet, where the hood is, was crafted by the carpenter.

The countertop was purchased and installed by a stonemason.

And was it all worth it?

you can buy "wood" and also install it yourself, no one is stopping you. However, I wouldn't go that far because it is difficult to prove the evidence "the front was delivered scratched" or if it was you.

As Kerstin already wrote, I would also have everything that directly relates to the wood installed.

You don't have to take the handles from manufacturer A if you don't like anything there. She wanted brass handles, which LEICHT didn't have in the program back then.

The big chunk was the cost of the countertop (quartz composite), she needed 3 slabs (3x1.2m). She went to a dealer who cuts, polishes, etc. the slabs (Caesarstone) in Poland. But there are also manufacturers in Germany that offer quartz composite and are significantly cheaper than the market leader. Hotzenplotz, who was also on this forum for a long time, bought his slabs from a cheap manufacturer in DE.

If you want these "special hot appliances," you have to buy them from a dealer because they are not available online. As I said, I bought one appliance online, two others were purchased through the employer, and the rest at an electronics store. Oh yes, the sink was bought through LEICHT, the faucet online.

I believe LEICHT does not do block invoicing, whereas Nobilia and others do, and separate purchase of electrical appliances then perhaps makes less sense.

So it was a mix

Roughly speaking, the all-inclusive package is only available if you buy everything from a single source. If you want to forgo that, you can also assemble any kitchen studio kitchen yourself (which is much easier and faster than Ikea) and get the appliances yourself. Dishwashers, and especially built-up dishwashers, are only for creative tinkerers at Ikea.
Not all appliances are available online; some are only sold through kitchen studios/authorized dealers.

If you get the appliances yourself, it is your job to make sure they fit with the chosen base cabinets/countertop/heel height, etc.

Actually, I don't want to buy the devices separately. That annoys me again.

Then just don't do it and get everything from one source.

So in my case, I would have saved 1000 EUR compared to the offer from KFB for 4 devices. I believe you are planning with more devices. Maybe with two to three hours of research, one can manage to procure comparable devices (not exactly the same), saving 1000-2000 EUR. That basically amounts to an hourly wage of 300-400 EUR, minus installation flat rate for external device installation, minus hassle with warranty.