Didn't realize Buch was that low now. Are any of the ramps closed from low water?
You can Google open ramps. I normally launch on the north end. Llano County shows open to 1003 which is about the current elevation. Burnet County is open to 993 but on the north end and not protected from south wind. I like Thunderbird by the bike park but looking at Google satellite it appears to be out of the water. I only fish Buchanan in May and June so can't help you with tips. I would think the upper end of the lake is best. At the current level you have to make sure to stay in the channel. There are channel marker bouys up there but spaced kind of far apart. You might call Buchanan RV Park formerly Big Chief. They are near the dam and have a good ramp. It is private and charge a fee. You might also look at the LCRA ramp near Tow on NW side but I am thinking it is not usable.