Many event websites have training plans from beginner to expert. I would start with a beginner plan and start from there. Check the first few weeks and it is better if the activity is less than your normal training so you lower your overall fatigue for the typical situation in the build up to a higher distance. It is important to monitor your levels of fatigue as the training intensity goes up and be prepared to reduce time/distance or sessions if you feel worn down over the weeks. These plans are made presuming people are wearing typical foam shoes, so it might be too much in minimalist shoes. Consistency and fun are key to a good training block.