We would need to know your electric rate per kWh, however based on the average rate in Ireland of €0.34, you should expect the following:

Cost to run 1 x S21 Pro per day: €28.64
BTC earnings per day: €13.58

Total loss per day: €15.06

Hosting companies are mostly scams - and very unlikely anyone would host one single unit like that. S21 Hydros require additional equipment, pumps, filters, water infrastructure etc. Typically you will need to invest in 10 units or more, purchased through the hosting company. But expect to get ripped off!

Your best bet would almost certainly be to invest in BTC and hold, rather than mining. As a general rule, you need free or very cheap electric to be profitable in BTC mining. That means around €0.05 per kWh or less

It is not by buying the best mining equipment and all. Have you thought about the other running cost? Do you have a facility to install your mining rig? What type of power do you intend to use - solar, fossil, wind? And have you calculated how much it would cost for each of these, the advantages and disadvantages running them based on your location? Have you considered some local laws and regulations with regards to bitcoin mining? How about human resource, what is your plan for it? Do you plan to run it alone or employ the services of someone else? These are the no-so-big but important questions you need to think about.

Also be aware - related to the above - that there are Windows viruses that do in fact change your pool settings in any miners they can find and point your miners to mining for someone else.

While standard manufacturer S9s so not allow this virus to affect your miners, a program like awesome miner has the standard option to allow such viruses to get into your miners.