If you want to work with mains related voltages an Isolation Transformer is defenately a big plus.
But as you say you are a beginner, it is probably better to not mess with mains voltages directly for a few years.
An isolation transformer is no guarantee for not letting some smoke escape from your oscilloscope or fingers.
If you don't work with mains related voltages, you have no need for an isolation transformer.
Get some extra multimeters.
You often want to measure several voltages at the same time, or monitor current & voltage.
These other meters do not have to be very accurate / reliable / expensive.
You can check them with your Fluke if there is any doubt.
The aneng AN8000 series is very popular lately.
The finding a good project is the hard part.
A watering timer is a very common piece of kit:
https://www.aliexpress.com/wholesale?SearchText=watering+timerAnd because water flow is relatively constant, there is not much use in adding a flow meter.
https://www.aliexpress.com/wholesale?SearchText=flow+sensorOn the other hand, If you buy a separate electrical valve (and possibly flow meter) you probably have much better quality components than the "watering timer" from the link mentioned above.
Seems like a doable project for a "beginner".
It seems that you do not have a function generator.
You can buy a fancy 10MHz+ version, but for starters it is always handy to be able to at least have an easy way to generate some kind of test signal.
This version with the ICL8038 seems a nice compromise between very cheap and usefull.
https://www.aliexpress.com/item/High-Precision-Function-Signal-Generator-Module-DIY-kits-for-Wave-Output-3Hz-300kHz-Adjustable-Frequency-Amplitude/32838770885.htm(put it in a box with a power supply, front panel and real switches instead of the jumpers for ease of use).