Get yourself some webbing off eBay. It'll probably be cheaper than a weighted vest anyway. Spread the weight out around the pouches with bags of sand. Can't beat 'training for the event' IMHO. Oh and don't do too much running with weight. You'll only knacker yourself and turn up carrying an injury.
Focus on getting your general fitness to a high level first (10km in under 50 mins is a good start) then begin adding a few weighted runs, just so, if nothing else you're confident you can run in boots with weight. Google some stretches for you lower back etc if your new to running with weight. The 2 most important things are 1 arriving very fit and 2 arriving without a niggling injury.
Ankle weights. No, I am not taking the piss. Nor am I a qualified PT instructor, but ankle weights? What? The human body is magnificent and basically a sprung structure, your skeleton. It is designed to carry weight. For a short distance and maybe at speed. But only if the weight is distributed high up so the impact may be absorbed by the entire sprung structure that is your skeleton.
Seems to me it is like lifting heavy things. We're built to do it, but regard how it will impact upon your skeleton before you do. Otherwise get used to limping and aches when the wind is from the west.
Not unless you train doing a thousand reps of tiny weights none stop over 45 mins. Running with weight uses muscles differently to lifting heavy stuff. Weights help you pull and look good on the beach. For what i'd call 'useful fitness', lots of running (and find some hills) swimming, press ups, chip ups, sit ups (using own body weight)
Im not a big fan of ankle weights,can be excessive and alter running form causing injury.wrist weights can be good though for runs up to 4miles,gives you an effect similar to a cross country skier of using 4 limbs.
don't bother with running with weight pre training, the risk of injury is high and its really not worth it. Just get some miles in your legs and keep the general fitness ticking over.
just make sure you can run a sub 9 min pft and your onto a winner.