To A, it's only possible to cast and then "hold" an effect from going off in conjunction with Time 4 magic. If you build a robot suit to serve as a focus for increasing your Strength stat, you're realistically looking at making that Arete roll every time you suit up, and maintaining the effect so long as you're fighting in it.
To 2, a quick look-over of Revised confirms that the rules for creating Devices or Wonders are not in the core book, but in the Revised Storyteller's Companion (p.53-65). For better or worse, you're still functionally rolling a 'forces attack' every time the ray gun (or power armor, or whatever) is fired, but there are ways to shuffle the burden off to others. Depending on who you want to be able to hand it off to, there are a couple of ways you could go about it. An Artifact/Invention would work for any mage whose paradigm is functionally compatible with your own; they have to still make Arete rolls using their own stat to use the effects, but don't have to have the Spheres in question, and the user suffers any relevant Paradox that comes up from its misuse (intentional or otherwise).
Charms/Gadgets are short-duration items -- the one-off battery pack and circuitry to power and calibrate your ray gun -- and when you turn them on, they work for the duration of the effect: instantly in the case of a single attack, or otherwise a scene or so before burning themselves out. They're useable in locations or by Sleepers whose paradigm is compatible with yours, though Paradox may apply if shenanigans start to occur.
Now, if you wanted a reuseable item that may just need recharging, you'd use the Talisman/Device category, possibly also simultaneously marking it as an Artifact. Mind, a Talisman/Device is still Doing Magic, and still has to make the magic casting roll for the effect in question (the raygun shooting rays, the seven-league boots taking seven-league steps), but in theory you could hand the device off to whoever you please and they'll get to use the 'fire rays' effect as they see fit (or so long as the object has stored Quintessence to burn on generating the effect). That said, because the object in question is still Doing Magic, it's subject to the normal rules regarding magic casting, so you want to keep this thing in locations or in the hands of Sleepers whose paradigm is friendly to yours to avoid the vulgar-magic-witnesses modifier to your object of power's casting rolls and subsequent fallout.