I rewired my first Triumph - one of my T160's - over the '82/'83 winter, followed the Lucas system and the electrics have been totally reliable; subsequently, I've also made the electrics of several old Jap bikes more reliable using the same principles ... The system I use was/is a simplification of what I found in the T160's original loom; I've used it ever since on every bike I've rewired:-
. Two '8-way' (four wires in each end) standard bullet snap connectors, one in the headlamp shell, one in the area under the seat;
. individual components connected to the nearest '8-way', including the battery 'earth terminal' to the under-seat 8-way;
. the two 8-ways connected together by two lengths of thicker wire, those two lengths joined:-
.. either at a ring terminal attached to an engine component (e.g. one of the head-steady bolts);
.. or at a '4-way' (two wires in each end) standard bullet snap connector above said engine component, with another wire from the 4-way to the engine component.
Again bear in mind, while your bike didn't have a separate "accessories" circuit, as standard it had separate circuits for ignition, headlamp, other lamps and horn. However, unless you're a habitual Idiot's Lantern user, you might find an actual "accessories circuit" is unnecessary - with standard 'original Lucas' colour codes easily-available, unswitched, switched-by-ignition, switched-by-lights and common supply or return wiring are easily-identifiable for connecting additional gadgets.
Fuses - is advising blade fuses stating the obvious?
The practical problem I've encountered with separate fuses for different circuits is - as both the switches that separate the circuits and the items they switch are mostly at the front of the bike - where to mount the fuse box/group the fuse holders without running lots of wires up and down the bike? Year or so ago, guy who posts on Britbike and I discussed this, and he was coming up with a small fuse holder using 'mini blade' fuses to fit in the back of the headlamp shell, but 'fraid I don't know how far he's progressed.
One fuse I most-strongly recommend is the 'main' fuse in the one-and-only wire attached to the battery 'earth' (positive or negative) terminal. For reasons now 'lost in the mists', '68-on, 'original Lucas' moved the main/only standard fuse from the battery 'earth terminal' to the 'non-earth terminal'; as you find in all the old-Britbike internet forums, hapless owners have found this later fuse position doesn't protect from an increasingly-common type of short-circuit ...
Because the main fuse is the solitary wire to/from one battery terminal (say battery +ve as standard on your bike), while individual circuit fuses would be connected to the other battery terminal (say battery -ve on your bike), I've often found it easier to using individual fuse holders that clip together - additional holders for spare fuses are easy to include and, if possible, fuse holders can be grouped easily.