People do not want to walk uncomfortably far in procession. Go at the pace of the infirmest and travel no further than they can comfortably walk. A hundred metres is enough.
It works best if everyone walks, because then everyone can see one another and feel the togetherness.
Choose a route which is free of traffic.
You will need somewhere where people can gather, having already parked their cars—at the gates of the crematorium, perhaps. You will need to do some research. If you live in an urban area it could be tricky, but if you live in a village it could be easy enough, and very picturesque.
You will also need to think about what order people should walk in, and whether you want anyone to walk in front of the hearse.
For a walking procession, the best kind of hearse is a horse-drawn hearse or wagon, or a hand-pulled cart. Horses walk naturally at human walking pace and give the procession a timeless feel. The drawback of a motor hearse is that it seems to go exaggeratedly slowly – to make an effort, impatiently, to hold itself back.
Instead of using a hearse or other conveyance you can carry the coffin yourself (with five others) but together you’ll need to combine strength with stamina. Several or many people can take a turn.