Looking for some general info on best times and places to buy sets

I’m not looking to flip Legos, but I would like to buy sets at the lowest prices. I’d like to get Rivendell, the Enterprise, Barad Dur, and Jabba’s Sail Barge in the next year or so. When and where should I get these? I get 5% back from Amazon and Target. I just got the ATST from LEGO so I am starting to understand the points and gwp sets. But the points will rarely be worth more than my 5% discounts at Target and or Amazon. Do sets go on sale right before they are retired? Any insight would...