A serious cruising boat should carry at least three different anchors on board, and one should be better than the other two for a particular type of bottom. I'm not a great fan of anchor-sizing formulas; if your boat is heavier or has more windage than an average boat of similar length, you'll usually need a bigger anchor than the one recommended by any simple formula. Remember, too, that holding-power numbers are based on ideal anchoring conditions, so if you're in ooze, grass, or gravel, the actual holding power may be much lower. I do know that the bigger the anchor, the better it holds. An anchor that's one or two sizes larger than the recommended size is perhaps the best way to compensate for real-world bottom conditions. No anchor ever dragged because it was too big.
All anchor rodes, even those defined as all-chain, must be some combination of chain and nylon line. An all-chain rode must have a nylon snubber line that‘s at least 20 feet long to absorb shock loads. A combination rode, with a length of chain shackled to a length of nylon line, also provides this intrinsic shock absorption. As for proper length, a 300-foot rode is adequate for anchoring in depths up to around 35 feet.