yep get an API master test kit, isnt THAT expensive (£30) for what it does, it WILL save your fish and you alot of money.
Dont add fish for a good 1-2 weeks
and that goes for EVERY time you add a fish or more than one, always give the tank PLENTY of time to adjust to the new fish and their bioload
Test ammonia, nitrite and nitrate EVERY DAY for the first 2 weeks without fail.
record all your results as then if anything spikes or goes wrong you can see where and when and find the cheapest, fastest solution to your problems should you have any arise.