1) Not usually. That would look a bit like wearing suspenders on the outside of your coat. Clipons give you the advantage of a tight, low riding position. For above the triples, you'd do better with straight bars or, as Drewpy suggests, Jota bars.
2) Cable lengths can be dealt with in 1 of 3 ways (that I know of.) 1. Let your cables hang out. Some of them can be rerouted to take up the slack, but too many bends and they don't work as well. 2. You can roll your own. I tried this. I failed many times, and then went with the last option: 3. You can call Motion Pro, or go to their website, and order custom cables. I think they're $20 a cable for the main hand controls, and you just say "I have a Seca 400, and need cables that are 7 inches shorter." Measure with string first, to make sure you leave enough cable. For the record, Motion Pro was excellent when I dealt with them.
3) The Seca tank may be narrower at the front, or have more clearance. The Maxim tank definitely did not. I've seen a couple of solutions, but they tend to fall into two categories: narrow the range of motion of your forks by narrowing the stops, or hammer indents into your tank to accommodate the clipons. Truly, you won't know for sure until you try the clipons on your forks, and see if they hit.
Oh, something else I just thought of. If you go with clipons, your gauges will look really lonely sitting on top of your forks. I was able to bend the bracket and move mine so they mounted on the bottom of my triple tree, but I was only able to do that because I replaced the headlight bracket too (to drop the headlight lower.) Try just removing your bars, or imagine if they weren't there, and think about how high your gauges will be.
Of course, if you lower your gauges, then there's two more cables, speedo and tach that are now too long...
As I said, it's not a project for the faint of heart, but also as I said, I love mine.