After over a week of playing Holybread.io, I have now finally met the requirement to unlock HeroSlot2 (Requirement is: 'at least 75 battles in Arena and have spent at least 1500 Energy in adventures/quests) and therefore I can now use 2 Heroes in arena. XD
Fortunately, I got lucky on my first 2 days and found myself 2 Heroes so I don't have to at least buy some Heroes in the market.
Since one of the heroes I have found is the same profession as my main one (another mage), I have decided to use the 'warrior' hero Bartholomew instead.
It's bonus skill '10% extra gold' is actually also pretty cool in doing quests. At one point, I got a quest reward of around 1000 Gold in just 1 quest. (Although I'm not sure if it has something to do with my main hero now at level 21 but I have been getting quests which rewards a lot of gold XD)
At the moment, I haven't equipped any equipment to my second hero but have already raised it's stats to at least 25-35. The current items that I have for warrior types are equipable around level 15 so it's still a long way to go for this hero to be of some use in my Arena matches. XD