Welcome to the club. if you havent yet, take a look at the LTT COC for more info on what is appropriate and what isnt. if you need anything we are here to help as best as we can.
if you do everything yourself youll probably be looking at around $300 and if you get a kit about $600 and a plug and play system will cost around $1000. good luck on your journey. right now the price is too high for me to venture down this road.
thats not how it works. its not so much trusting their specs as much as you are trusting their life span/warranty. the higher priced ones will generally last longer than some cheapie.
plus it looks like that pump is for a fountain and its fittings are not barbed or compression so you might get some leakage over time.