I have looked for the pad spacing in the documentation but was unable to find it. I will measure center-to-center on the pads, but I won’t be with the VIM3 for several hours.
I mentioned that excessive heat could damage the PCB, but this is true for practically any modern PCB. If you have experience with soldering, it should be OK. However, if you are new to soldering, I would try to find someone with experience, or an electronics repair shop, to solder leads on to the XPWR pads for you.
Proper tools and materials should be used, such as flux+electronics solder or solder paste, as well as a temp controlled soldering iron or hot air. That being said, someone with soldering skills could do it with a regular pencil type soldering iron.
If you have an interest in soldering and you have the tools(not expensive), it is not so difficult. Plenty of Youtube videos to help learn soldering, I assume. Find some old disposable electronic devices and practice soldering until you feel comfortable about your ability.
I have no experience with the silver adhesive you linked to. Personally, I would be reluctant to use an adhesive. Among other things, adhesive could complicate rework should the area need work. Devices mounted in a mobile environment can be subjected to vibration, impact energy and sustained high heat, I have no idea if that adhesive would hold up well in that situation. If it conducts adequately, it might work, while I would not try it, the decision is yours.
Anxious to watch as your project advances. Layout looks great.