Some question before investing in a mining rig

Dear all,

Before investing in a mining rig, I write down some questions considering that we can read positive and negative opinions. Please do not feel to answer all the questions, I will chase some answer in other topics if I found it and thanks you in advance for your answers.

Buy a refurbished machine
- Advantage to begin right now to mine
- risk that GPU or parts broke just after, what would you look at (or ask) before buying ? Will you buy one ?
- risk that firmware has been modified and tokens will be stolen in the future ?

Buy a ready to go machine
- need to wait long time before beginning to mine
- Risk that software/firmare is modified, how to check integrality ?

Build own machine
- long wait for material
- issues with configuration and possible risk of introducing breaches for easy "hacking" ?

Software, pools
What mining OS/software will you recommend ?
Which pool will you recommend and what are the risks and fees ?

Crypto to mine
Website to see which crypto is more profitable ?

eLearning
Is there a site explaining deeply from scratch the crypto world ?

Rig location
Is it possible to install the rig in the balcony if it is protected from rain ?

Profitability
Trying to estimate profitability, I used different websites, but I'm not convinced they calculate correctly as changing parameters does not change profitability value (i.e. hardware cost or take account difficulty). Did you see correlation between your real gains and what was predicted by the website ?

Mining vs Trading
I'm not a trader and I'm wondering how trading can, for the not trained traders, be better than mining. With the rig you generate tokens that, if websites are correct, cost 40% in energy, so you still have 60% free tokens and ROI of a rig around 6-8 months depending on the various scenarios. If there is a crash of crypto value you still have some material to sell so your rig will not be 0 value.

Goals
The idea is to mine and used the crypto mined to pay electricity fees of the next month (lost of the first month of electricity as risk), keeping the other part of crypto in a paper wallet and wait that crypto become a real market used everywhere like VISA card. The only risk is then, the investment for the rig that I lose. The key is the to choose what rig I can buy with the money I'm ok to lose in case of crypto is just a "scam".

Thanks for you help again and sorry if question appear to be too easy. I think there are fundamental before doing anything and it is not clear to me yet.