Piece o cake. I `ve done this.
first guestimate volume required for bladder and struts . I came to 297 litres for a RRD type z 13.
Find out what your filling supply is rated to. Ie some dive shops only fill to just over 200Bar...some 300. Private folk can get upto 400(but tank is probably flammable gas tank) I would not recomend.
choose your tank .Aluminium is lighter and often to 220 bar unless going for O2 tanks. Steel heavier but can do 310bar sometimes more.
For tanks there are only 2 main manufacturers worldwide...Luxfer and Faber.
Choose your tank valve(pillar) ...A clamp or DIN(A clamp not usually rated fro more than 220 bar)
I used a cut off charge whip straight from an A clamp block with no reducers for simplicity and the only control being the pillar valve.
But from there onwards you can have inflation valves off reducers(1st stages) etc. and whatever you require will be on the market. DIN fittings are a bit more limited in fittings and costly.
I keep it simple and lightweight as possible
Works fine but a bit of a gimmick if your back is OK
dont leave your bottles in the heat/sun
Lastly...if you get your bottle/ filling pressure just right allowing for spillage and have around 30 litres left in the tank and your mates are buzzing around well impressed. Tell them they can have a shot after you if they put it away for you:D