Hi @DavidSkodt, good to hear that you're ready to start testing. Let me start off with your first question:
Wrong question to ask :). You don't select the approach and methodology in function of the tools that are available, you select your tools and approach in function of the research question you want to answer. So in this case it depends on what you want to figure out. Usually researchers tend to restrict usability tests to an hour, because of the effort that is being asked of participants. Guerilla testing is more of a style of conducting your test, and it not opposed to an hour long test. You probably want to compare a guerilla test vs. a lab test. I personally favour a guerilla test, because you can conduct the test in a more informal and natural setting. With a lab test you always have the simulation effect, which influences your participants a bit, and thus influences your results.
Usually the consideration is made based on both available resources and the insights you want to gain. My tip is, don't overthink this process, just do it, and learn. Nobody nails it from the first time.
To record a session on mobile, I always used Lookback, which is a very good tool. I heard they removed the integration with Invision, which would be a pity if this is true. Also, ask yourself, why do you want to record this? Is it needed for your process? Do you want to convince stakeholders with raw footage? Given that this is a portfolio project, I say again, don't overthink it. Don't let this slow you down, or stop you. You can ask a friend to take notes on the fly, which saves you a lot of analysis time in the end (trust me, you don't want to go through all the raw footage again).
My general advise is, since this is a portfolio project, adopt a hands-on approach, and just try out things. If your first round of tests didn't go well (in terms of process), what's stopping you from doing it again? Trial and error goes a long way, and your process is more valuable to your portfolio than the results.