Delivery / Assembly of garden houses – Digital speedometer over 3.5 to?

Hello! We are currently selling our garden houses only from stock, on pickup. But now thanks to Aunt Google more and more inquiries are coming which are currently up to 350 km far away (e.g. Freiburg or Odenwald). We are in Munich. But also the first inquiries and first orders from Switzerland and Austria come. All these orders are assembly orders. Only we would not deliver so far, this can certainly be easier and cheaper for a forwarding company. If I now calculate: Roterschemel trailer max. 3 to. – Empty weight 770 kg (available) Our load – max. 2 to. car (on-site car?) e.g. VW Touareg (approx. 2103–2315 kg) – Towing load 3 to. makes together about 5085 kg So clearly above the 3.5 to. How can I get this together at the most cost-effectively? What does a “digital speedometer” cost into a used vehicle? Are there monthly costs? What do I do with normal trips – without trailer to the customer? Can I use the car at all still privately or is it just my “delivery car”? What about “works traffic”? I am building up myself. Or is that already commercial freight traffic? Do I have to take care of the German toll system? Questions about questions – I hope you can help me a little bit. I have read a lot here already, the confusion has not become smaller…… Thanks already AFlurry