Generally speaking, being melee magicka based would mean to use the class and mages guild skill line with your weapons more as utility or a stat weapon.
Using dual wield will in itself increase your spell damage as it is tied with your weapon damage. I'd imagine that you would use dual wield for the mobility (blade cloak - quick cloak) or for snares (twin slash - Rending slash) and leave the main damage hitters to concealed weapon, inpale, funnel health. Its really how your type of gameplay is, you don't need to do a stealthy char just because its a nightblade.
You can go balls out blood sucking magic wielding impaling magicka warrior that uses dw and destro staff for moar dots, MOAR DOTS.
Ahem.
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DW magicka melee nb will most likely not use any weapon abilities except restro or destro staves. A common setup is DW/Restro
Bar 1 key combos teleport strike/concealed weapon/soul harvest/impale/dark cloak DO NOT morph teleport strike. Lotus fan is generally awful for a magicka melee nb. I tried to make it work even with a skoria set but you are better off front loading all your damage as best as you can.
Bar 2 is often escape and evasion with a little range attack so Restro: Healing ward, efficient purge, shades, mist form, etc. You can experiment to see what works best for you.
Do not neglect magicka regen. You will never have the raw burst that stam has so you need to be able to engage/disengage and control the fights on your terms.
Not sure if siphoning attacks is worth it for a stam build. Generally in PvE you can law down twisting path, toggle SA and then sap essence over and over. Sap essence is a magicka skill.
In pvp Sap tanks used to be pretty powerful. I don't see as many now but I never used that build and am not really up on it.
I can tell you that a siphon build is possible for pvp but it is usually magicka based. Stam builds can generate high regen with way of air, werewolf, night blade passive, bosmer etc. The magicka builds that I have seen put siphon attacks on one bar and toggle it as needed to manage resources. Takes a fair bit of skill.