I used to do the same thing,

Here's what I did to keep me on track last year and it's helped me out loads.
Dec-Jan: All options are on the table. I go through my links, saved pictures and
'Fix list' from last year and write them all down on one sheet of paper divided into the room categories:
Spider room, vampire room, driveway, graveyard...etc. Then I look at projects and decide which ones of them I really want to do and then write the
'master plan' for that year's Halloween.
With that done, I decide which of the projects is
a) what I'm really excited about and
b) the most time-consuming or so new that I have no idea how long it would take. I do that project first with no time constraints.
Then, when completed, I see if I want to add any other projects that may have been brought up here at the forum and add them to the
'master list.' Now, I make the time-line for the other projects that I know basically how long they should take. I do the ones I want to do the most first and the
mildly interesting ones at the end. If I run out of time, that was okay, wasn't that interested in it anyway.
Aug: I rewrite my time-line to better reflect projects left to do. Then, I try to stick to the plan as best I can. With Halloween coming so fast and the time-line it helps keep me motivated to stay on course.
October: I begin pulling my hair out because for the life of me I always underestimate how long it takes me to do projects,
UGH! But, that was okay 'cause hopefully I'm down to the projects that I was mildly interested so in the end I can stay sane.