Seeing as you haven't said you solved any of the problems, here is the general stuff:
I think it's a given that you need hyper triggers to make sure the bombs go off at the right time

1. Place invisible units on all the squares that are blockages, for comp 1. I think the bomberman game uses a sort of half checkerboard of these.
This will allow you to detect when one of the directions is blocked and prevent the blast.
2. Place another type of invisible units (i keep saying this... I mean stuff like observers, and any zerg ground unit that can burrow) Again for computer 1.
These will mark where bombs can blow up. To place these neatly fill the board with computer owned pylons and use a small location to replace them all with the hidden unit. Of course other 2x2 buildings will work too.
I estimate you will need 3 computers for this, all neutral. This way you have enough to get some decent stuff going. It's not like there's stuff that can attack, and 5 players is more than bomberman should even have still.
3. Explosion sizes. These would be 1x(x) & (x)x1 locations in varying sizes that can be used to trigger the explosions. The fortunate thing is that lots of the following triggers need to be made for only one of them, as follows:
First, center the locations on the bomb
Next, check to see if either direction is blocked by control at the location of invisible units.
Then, give all the units owned by computer 1 to comp 2 in any (or all) directions that can be blown up.
After that, center 2 map-spanning locations on the bomb. This will allow you to use the computer owned units for effects.
3. Stuff blocking the path. I think it would be best to use a computer 2 controlled building, rather than addons which I did. I didn't bother to make the explosions stop when they hit the addons, but this would be quite possible with computer players, though a little complex.
First off, you would want to center your locations as above.
Then, for units owned by computer 2 in the location, give them to computer 3. You need to do this so that any blockades will notify the triggers of their presence and get some conditions going. Another notification will occur when it reaches the bomb, as this tells the game whether there is a blockage before the bomb (centering locations on any unit at a location go to top left preferentially from what I remember). If there is a blockage after the bomb, it can stop there more easily.
Once you know if there's a block in front of the bomb you can start blowing

up (ah, my favourite). I'm sure you can figure out what to do with your conditions, by giving the comp 3 units back to comp 1 and executing players who happen to be there at the same time. I suggest having a switch set if there's a block in front and clearing it when you pass that block. At that point you can start blowing stuff up instead of just giving to comp 1. Of course if it reaches a bomb it can just set that bomb's delay to 0 (on the note of bomb delay, I think a rather nice way to do this is to have a few locations for each player with switches telling whether they are in use, and having them terran missile turrets with low hp that blow up on their own, vacating the location and making stuff happen) If you follow that you can just kill any bombs and let them take care of themself. If you hit a block once the switch saying if there's a block in front is clear, you just blow it up and give all of comp 3's units back to comp 1 and the explosion is done. Duffman says ooooh yea

When you remove blocks, you want to create a couple invisible units there - one to mark it as explodable and one to mark that it used to be a block.
Upgraded blast range> center bigger locations, thus give more units to comp2.
Number of bombs> enable more of that player's bomb locations.. I figure if you make turrets cost 1 and then give them 1 mineral when a bomb blows this should be good. Then give them another min if they have enough bomb locations.
Extra life> pretty simple, follow them with a location and if they die create them there (or their home spot I suppose without a location following)
Slow down> moving a unit next to them and then away successively in a trigger slows units down even though they don't see it.
Lay bombs behind you> This would be pretty simple to do, I don't know how often you would want it but you could have a death count for every time they pass over a marker unit so they move 3 squares and get it planted or whatever.
Short Fuse> If you use decaying turrets, the easiest of all. Just spawn them with less life.
Teams: These shouldn't affect the gameplay in terms of triggers, they just change strategies.
Rounds: You may want to use invisible units created as blocks die to respawn them. Just center on the invisible unit, kill all units, create a block.
It's fun refreshing and watching my posts per day drop as it gets longer since I registered.