The important thing is that you're in generally good shape (I assume) and that you have quite a bit of experience going those distances, even if it's only once a week. You know not to push it, to drink before you get thirsty, and so on. Other than that, the main thing is to take care of the minor problems before they become major (make sure the bike is in good shape before you go, avoid sunburn, treat chafing and saddle sores with Bag Balm, eat well, sleep well, wash up when you can, and so on). Also remember not to stress out if things don't go according to plan; you can almost always work it out with some thought and persistence (and maybe a little help now and again). You might be a little sore after four days, but that's about it. Good luck.