I began potty training about 2 mo. ago.
Hello turnnurn,the diary is a good idea,locking him in the bathroom is not,this could cause him to think of it as a type of prison for being bad.
Start having him sit for both pee and poop,the standing to pee is one of the major problems with poop training,he has been standing to go in his diaper since birth,so we must put a stop to it if possible.
At night he has no control over his body,so I would tell him his pull-ups are for night time only,and have him wear his regular trainers at all other time,I have done so many times,but being old fashioned,I have them wear plastic pants over them whenever we leave the house or have company over to save the clothing and furniture.
I hope this helps some for a start.
Please keep us up-dated on what you try and his responses.