1- travel (compression and extension) will vary. compression on how stiff the shock you end up with is in comparison to the weight of the car, extension on how short the shock is.
2- you shorten the strut tube to suit the length of the shock body, usually a little longer than the length of the body so that you can pack under the shock to ensure it screws in tight.
3- shock choice ??? hmmmm ... depends what you're using it for ?? koni yellows ... not cheap tho i'm just using 240z pedders comfort gas. alot stiffer than the 1200 shocks as they're designed for a much heavier load.
4- you can drop the spring seats to lower the car and keep more spring compression/travel rather than getting shorter springs, gives a better ride in regards to harshness and spring bind. only thing with lowering the spring perch is you can only really lower it as much as what you take out of the strut body otherwise you'll be back where you started in regards to bottoming out.
5- no idea on the Maddat kit ?? cant log onto their site still ??

what struts are you using now ?? the 200b struts are shorter than 120y and stanza bodies, the spring seat needs to be changed as it's a bigger dia than the stanza/1200 one, but i think from memory the body is about 40mm lower than the stanza ?...
here's some shock lengths :
stanza insert - 437mm
200b insert - 402mm
240z insert - 378mm
.... so the 240z insert is 59mm shorter than the stanza one



you can see the amount cut out above, when i did mine. you can also get an idea on spring seat location. left is a stanza, right is the chopped one.

hope this gives you a starting point