As a narrow-boating newbie, from the world of sail and motor-boats (with several years based on the Thames), might I pitch in?
In challenging conditions, I'd suggest you need two anchors, both with decent lengths of good, heavy, chain. The boat lies to the friction between chain and bed, not to the anchor, and the anchor is there to hold the end of the chain in place; a rope rode is inadequate other than in very low-load situations. Why two? One (the bower) will hold the boat from progressing downstream, the other (the kedge) is deployed from the stern, to prevent swinging into the fairway or into obstructions etc.
If your boat is too long to swing in the width available, and you're making way downstream when you need to go to anchor, you would of course need to use the kedge as the bower, and vice versa, so this needs to be a deciding factor in the size of your tackle (no sniggering at the back!).
In my experience, a decent kedge set-up is a great help in mooring with the bow against a small access place on the bank, as one can hold the stern precisely in place and often make a mooring where none was apparently possible - this can be very helpful in busy spots, and achieved many good nights for me on the Thames. Of course, great care must always be taken not to obstruct the fairway, but it's worth noting that with that proviso, it is perfectly in order to anchor on the non-tidal Thames, though you'll need to be prepared for rowers to collide with you, as they don't expect boats to be lying at anchor, and their look-out can leave something to be desired. The perfect set-up has powerful winches at both bow and stern, but that may be going too far on a NB, unless you're going to visit strong currents often...