I went from keyclone to ISboxer so I'll try and answer some questions

1)the way isboxer does macros, you might be spending a good portion of time setting up keymapping in ISboxer. ISboxer does assisting following and other things within the program so some macros might need to be changed, expect at least 1-2 hours setting this up but once its setup, it runs really well

2) multiple computers works with ISboxer, with 1 subscription you get to use 5 computers so no problem there. There is a problem if you are using something like synergy or octopus to use 1 mouse across multiple machines. It doesnt like to follow when you go to a different computer. So if you are on your main monitor and switch to a second computer to control, the toons on your other 2 comps wont follow. There is a work around, but it requires more fine tuning within ISBoxer and if you have long character names, 1 character might get left out. ( check the isboxer forums for more info on this)

3) I still use keyclone, but for certain characters. I use isboxer for my pvp characters and keyclone for pve. You could use the same characters on both, but might run into problems with macros. using different specs for different programs might get around that, or using different bars.

4) I really like ISboxer for pvp. I was having lagging issues, and assist issues with keyclone in pvp so thats why i tried ISBoxer and really like it for that. for PVE, i didnt want to take the time to redo keymaps in isboxer for all my different characters so i still use keyclone for that since i dont have any issues in pve with keyclone.

Hope this helps