FIVE YEARS AGO, my husband and I bought 8 acres in southern Alabama, and FINALLY we have retired and moved to our little hobby/homestead farm. We've ordered our first batch of a dozen or so chicks (some brown egg layers, a few olive egg layers, and 5 guinea hens), and expect them by mail at end of July.
4 weeks old can be a bit early to be out without heat---I use brooder plates and they are usually very hardy by that age. Heat lamps seems to make them less heat hardy.
You should be fine though given the temps where you are. Just watch them

Maybe the folks on the guinea forum can advise regarding keeping the chicks and guineas together - https://www.backyardchickens.com/forums/guinea-fowl.45/
This is a useful link relating to guides to read through - https://www.backyardchickens.com/forums/website-announcements-feedback-issues-guides.3/?prefix_id=3
You can use this link to contact members in your area - Find your State's thread.

This video will help you learn how to navigate this site:
<iframe width="420" height="300" src="" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>