This is very important once you realize you can't bend over to pick things up from your bin.. I can suit up by myself with the exception of the snaps that connect my shoulder bells to the shoulder straps. When I wear Fett I need at least 2 people helping for some parts..
Members updated. Columbiamo - you have 501st status, but I don't see a TK listed in your 501st profile. When it's updated I will change your status here.
The time to build will vary greatly depending on the time you have available and how much help you have. While an experienced builder could probably take a suit from the box to finished in a few days if they were really pushed, I'd budget at least a few weeks to a month+. That leaves plenty of time for measuring twice and cutting once, as well as looking at references/asking questions here in between.
I'm not aware of any 3/4 sized suits. The screen-derived suits are smaller than AM or RT-Mod, but the only think smaller than that I'm aware of is TM's child armor and that's not readily available. Probably smaller than you're needing too..
If the helmet is getting stuck on your shoulder bridges, you might be able to heat and bend them lower so they're out of the way. Another option is to add some padding to the top of the helmet so that it sits higher on your head and further from the armor.
Sorry Walton, but even if you could receive the armor before Halloween you'd be hard pressed to assemble it to be ready for the 31st. Especially if it's your first build you really need to budget more time for the construction. I'd say a helmet could be done before Halloween, but not the whole suit.