Is God always "just"?

[Watson]

1) there is no reason why ominpotence is trumped by being maximally good (it is just assumed), in other words if god were free and all powerful why couldn't he do evil (biblically it seems more consistent to assume he can indeed commit evil)

Neither omnipotence nor being maximally good are trumped by the other. No one said God can't commit evil. He created it, He is capable of anything. That is the key difference between man and God.

Romans 3:23
"for all have sinned and fall short of the glory of God."

God chooses good over bad every time. Humans don't always choose good over bad.

2) if god is perfectly free and also only ever able to choose to do good, why could he not bestow that on his creation/s. We apparently are free but can choose to do evil and god lets us! (at least if created in his image why don't we possess his characteristics?)

We possess the knowledge of good and evil, just like God Himself. We are absolutely free to choose good over evil, any time, just the same as God...but we don't. We fall short of His grace.

3) If god is compelled only ever to do good, why praise him for it?, he has no choice (like an unthinking machine)

I don't claim to know God's reasoning for choosing good, I just accept and am grateful for it. I thank Him for it. I trust that His choices are higher than mine and that He makes them out of love and compassion. He is not forced in any way.

4) Imagine a perfectly evil god who allows people to freely choose to do good? Most likely we could bootstrap such a diety into existence with as much logical consistency as the Christian concept and it would expalin just as much about our world (nowt!). So why would that be less valid tha the Christian concept?

I can't tell you that God isn't evil because I don't know, but from what I have seen and experienced, there is a God and He is working towards our benefit.

The most likely explanation is that there is no such god with these properties

You just committed the same fallacy you agreed with me has been made before. This is a non-sequitur argument with no basis for connecting the two arguments.