Hi i put my DD1 into her "big girls bed" at 18 months for the exact same 2 reasons. We not only got rid of the cot but changed her into a diff room completely. We painted it and got the bed made up etc and kept telling her it was her new big girls room etc. I was going to wait until i finished up work before putting her in their but one night half heartedly i said "do you want to sleep in your cot or big girls bed tonight?" She went straight into her nursery grabbed her cot quilt walked onto her new room stood next to the bed and said "up". Even though she had a new big quilt etc i let her use the cot one that night and we had no probs i tucked her in and she slept through as normal. I think making a fuss of the new bed and room before hand really helped as she was excited by the change also me giving her the choice that night and not demanding that she go in the big bed helped. We have had no majo issues since and she is now 22 months. She did go through a faze of if she got up early she would entertain herself by emptying her drawers etc and trying to get dressed. To stop this i put a small desk with some books in her room. I never have a prob with her getting out of bed at night but she will always get off it in the morning and play for half hour before i go to get her. Friends from playgroup dont like to shut the door to their toddlers rooms and have them hopping into bed with them throughout the nights or exploring the house in the mornings. I personally shut DD's door but she still has a monitor in the room. I think when she can open the door and let herself out i will be putting a gate up as i dont think she will come and get me but go exploring and she likes to play with my oven etc.
Good luck i hope it goes as smoothly as our transition did and i hope i havent rambled too much