Drop the Razer DeathStalker it's an Membrane Keyboard.
Mechanical switches keyboards are definitely worth it, for beginner if possible you should get feel for which switches you want in keyboard.
For gaming I recommend the
MX REDs (be wary they are linear and have actuation point of around 2mm and 45g, so they are easily pressed, quite bad for typing).
MX BROWNs (tactile swtich, with same actuation point as RED, good for gaming, lot better for typing than REDs)
Then there are MX BLUE (with tactile and clicky feedback, which totaly depends on your subjective personal preference).
and MX BLACKs (same as REDs just up to 60g actuation point).
To be honest it's quite hard to know what Switches you want without trying or hearing them beforehand.
You should google some differences between those switches on YT or somewhere.
But otherwordly, I would recommend the MX RED for gaming, very easy to double/tripple/four tap, or the MX BROWNs they are also quite good for gaming, but not quite as good performing for triple/fourth tapping, no problems with double tapping though.
I personally own keyboard with BROWNs and like them more over REDs.
My recommendations for KB would be:
Corsair k70 / k95
Logitech G710+ (only Brown)
Das Keyboard Professional
CM Storm QuickFire TK/Ultimate (they have different models)
As for mouse DeathAdder is very good mouse for performance and sensor part of it, but mileage and build quality can vary.
Some have better luck than others with it.
If you look into MMO/RPG gaming, it's also worth getting mouse with more keys on it, really appricate that for Key bindings.
Other good mouse at that price point with good sensors are Logitech G502, Logitech 402, SteelSeries Rival.