The reason I had a pH crash was because I was overstocked and very lazy about water changes (once every 3 to 4 weeks). Both of those allowed nitrate and other acidic things like fish hormones to build up. I have a KH of 3 German deg, and it got used up leaving nothing to buffer the pH so it dropped.
I learned my lesson and now do at least 25% water changes every week without fail.
If you use something in your tank made of calcium carbonate, that will help the same thing happening to you. You could use paddy's substrate or crushed coral; a piece of limestone or tufa rock (like fcmf) as decoration, or shells. They'll all dissolve slowly increasing both GH and KH.
If you don't want the expense of buying your own GH and KH testers, you already know the GH from your water company's website and you could get a sample of tap water tested for KH at a fish shop. If it is the same as mine or above (3 german deg/54 ppm) you'll be OK with weekly water changes. If it is below 3, I'd think about those things I suggested above.
The API master kit contains everything you need - pH and high pH (you'll just need one of those depending on how high or low your pH is) ammonia, nitrite and nitrate. The nitrate instructions say to shake bottle #2 for 30 secs before use and then shake the tube for 1 min before starting the 5 min timer. Shake the bottle for longer than 30 secs, and tap it on the worktop as well. It contains a reagent that settles out on the bottom; tapping breaks it up and the shaking is to redissolve it. Not shaking it enough is the major cause of inaccurate nitrate readings

As for ammonia, you won't need much with 46 litres. I get my Kleen Off Household Ammonia from my local DIY shop, but that comes in just one size of 500 ml for £2.50. Homebase used to sell it in their stores in the home cleaning section - if there's still a Homebase near you. Failing that, Ebay and Amazon. There is one seller on Ebay selling bottles of super concentrated ammonia for fishless cycling - it's 35% ammonia while most other solutions are 9.5%.
If you get 9.5%, you'll need 1.45 ml for a 3ppm dose and 0.5 ml for the 1ppm smaller dose; with that 35% solution, you'd need 0.39 and 0.13 ml. You can get baby medicine dosing syringes from a chemist shop to measure amounts that small. Remember the baby medicine bit - I got a very funny look when I asked for just a syringe

Have you added the bicarb yet? You need 2 x 5ml spoonfuls for 46 litres. I recently did a fishless cycle in a 25 litre tank and found 1 spoonful was plenty for that size.
To start the cycle, you need:
- water
- dechlorinator, also called water conditioner. This is to remove the chlorine or chloramine the water company adds to kill bacteria, and you don't want it to kill the bacteria you'll be trying to grow
- ammonia, and a syringe to measure it with
- test kit
- thermometer to make sure the water is in the high 20s for cycling. The kind that go inside the tank with red liquid inside are more accurate than those stick on the outside ones. Very few heaters are calibrated so that the number on the dial = the water temp. Most are a few degrees out. Go by the thermometer not the heater setting.
That's enough for one post or you'll suffer word indigestion
