we i dont ever plan on the big mek getting out of his wagon, lol and if he dose then hes dead to me for the most part.
not a big fan a large units of lootas. they are a huge target! and its very hard to get them into cover and make sure they have LoS. a small unit can still do some damage are easy to handel with out then getting blasted of the table for the start of turn 1.
Well your valuable mek is dead and no more force field protection for nearby vehicles. I've had my mek out the wagon before and locked in combat, I've had other wagons nearby which still benefit from the KFF - yours wouldn't
Indeed they're a huge unit and getting into cover can be tricky, just make sure you have a big crater or terrain! Though I found units of 10 to work fine, really. See with lootas it's volume of fire power, if you take 5 the most shots you can get is 15 and the worst is 5, not very good considering you need 5+ to hit and then on most transports you need 5+ to glance. Not good odds.
So while what you said about them is true, taking them in small units has more negatives.
No, if you only have one weapon, then weapon destroyed, immobilized, dead. You're giving your opponent the opportunity to take out a BW with STR:8 weapons. for 15 points, make him do Immob, WD, WD, WD, WD, then Destroyed!
Wagons are open topped so won't get many weapon destroyed results all in all. I wouldn't invest any more points in them then I'd have to. Keep them cheap!