First of all, I would question the wisdom of buying parts well in advance of building.
Over time, parts usually get cheaper, and newer, more cost effective parts are launched.
Never mind that your needs may change.
If you do buy in advance, stick to those parts that do not get obsolete quickly.
Like a monitor, case, psu, keyboard, mouse.
I would defer on hard drive/SSD because they are constantly dropping in price.
For cpu/motherboard/ram, new products may well arrive.
Some parts are dependent on others.
For example, the psu wattage needed is dependent on the graphics card selected.
The ram is dependent on the motherboard model.
In the end, I don't think you have much to worry about.
Most products will have at least a year warranty. Some will be 5 years, and even some lifetime.