Dell memory upgrades are always "well overpriced". Go with Crucial/other if you can.
If you want to upgrade storage, go with 250GB or greater SSD. (Most modern SSDs show maximum performance at 250GB and greater drives due to maximum "parallelism"... which is due to the size/number of storage chips.)
No "routine part" upgrades will void warranty. However... if you want to claim warranty service, you may have to restore the computer to original condition. (Dell Support isn't going to warranty non-Dell upgrades... nor should they.)
Better than "upgrading components", suggest buying used with the specs you require.