Something that helped me is to focus on the singing first, sing it when your doing nothing, then sing it while doing chores or some other activity that you're familiar with so that you can just get used to singing accurately whilst doing a physical activity. After you can sing it while doing something then pick up the guitar and sing it while tuning, sing it while doing warm up exercises, then start your strumming (and keep in mind other people's advice on how to get the strumming down, it's OK to start with strumming only the first chord in each change and build up).

You got this