any advice about collecting
Buy what you like to look at and what you can afford. Don't listen to anyone else.
Shop around. There are a ton of reputable online 1/6 resellers beyond Sideshow. Keep an eye out for coupons as they can also save you money.
Preordering isn't necessary anymore since figures rarely sell out before release nowadays, but if they do, expect to pay higher prices for them on the secondary market (unless it is a HT Force Awakens Stormtrooper; they can't give those things away).
Don't throw away original packaging or shippers just in case you have to sell any figures. This way, when you sell them there will be a better chance of getting your money back.
any advice about maintaining
Visit the individual threads for the figure. They are usually full of advice on how to deal with potential issues. Also keep them in a display case, away from sunlight and, if possible, room temperature with low humidity.
Most people use IKEA detolfs, other IKEA shelves, or spend the extra coin on custom glass showcases which can cost many thousands of dollars.
Hope this helps. Welcome to the [very] expensive hobby of collecting and modding 1/6 scale figures.
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