I think if I'd done that with the lighthouse, people would have run back and forth without realising they could climb. Plus they could then climb up the inside of the blocks, which would be daft. Similar problem with the cliff. Either way, it's possible to jump down from either area and work up to it again, if you really want to.
This was only a little level and designed in such away that hint signs explaining some of the features would have broken the immersion. I'm so hooked on the level editor that I expect to use the mod for any other level I make - including sequels to 'Do Not Pick Up The Key' and 'I Dreamed of the Sky' if I ever feel the motivation to make such things ('Ok, Pick Up The Key' - if only I could get someone to draw some cartoony cutscenes for me I'd be at it already).
I've no idea if levels made with the mod can be played without it if they don't use any features from it - I'm sure Ego can field an answer to that, though. Either way, if using it for a different style of level, I'd endeavour to explain one-way ledges and any similar thing if they cropped up.
I watched the director's commentary for 'Portal' a long time ago and it gave me a lot of good ideas. Using visual clues to represent certain features as a way of teaching the player to look out for something, or building the graphics to guide the player the way they need to look or move... They're techniques I try to use in my design; thank you Valve!