Hi and welcome!
For starters, I suggest to play the game for 2 weeks, experiment make mistakes, make lucky guesses and get a feel for the game. Do NOT spend any money. After 2 weeks you should have a decent grasp for the game and if you started a new server you should have a good feeling about the metagame aka what is being used a lot and what not.
After this, start on a new server with all the information you have and the amount of mistakes you make will be minimal.
As completely free to play (vip0) you will have to prioritize and you made the correct call to go for raid/hol (aka the pve elements of the game).
Early game hol is different from endgame hol (post lvl 90) and is sadly largely determined by luck, as you can get a goram from CoF or diamond pulls and that will make you HoL king for a good while even at lower levels.
You can also pull most 2 star heroes from gold pulls, so I personally would not hardsummon them (30 SS) unless you really need too.
Heroes you want from the gold chests:
Zem, Kong, Tashi, Garrick, Valan, Osiris, Tanya, Bloodspear and Taurus.
Heroes you want to farm with heroics: Osiris, Alana (she is the backup plan if you eventually keep missing out on the better heroes. do NOT hardsummon her! Just farm her SS and wait untill you pull her card from CoF.)
Heroes you want from the arena shop: Nilya (buy SS untill you can hardsummon then get to 5 stars asap), Valan (Try get his 2 star card from goldchest, after you have the card get him to 5 stars asap)
NOTE: Make sure to not farm them at the same time! Valan to 3, nilya to 4, valan to 4 etc.
Heroes you want from the CoF shop: Tashi, Zem, Taurus, Kong, Lingling (hardsummon her and then do not buy her again untill previous heroes are 5 stars)
NOTE: look at note above!
Heroes you want from the HoL shop: Tareth (Only because she is one of 2 tanks you will need to clear female dojo, hardsummon her and get her to 5 stars) Malrath is probably the best hero to buy in the HoL shop but he is mainly pvp and he won't help you clear anything else. On a sidenote Tareth can be used versus Firehawk in the Prophecy pool.
Guild coin shop: Mirielle (hardsummon and get to 5 stars asap) Honorable mention: Jasmine... but she is very weak and is no longer really needed for cof... but if you have issues with cof she is the one that will solve those issues. Driller is not good without awakening and his skin so as f2p I would not invest in her. Firehawk is good untill 80, he will be a major advantage in early pvp but a major disadvantage in longterm as past 80 he becomes TRASH! Bloodspear is a decent investment upto 5 stars AFTER mirielle is 5 stars.
Heroes you want from HoL shop: Garrick, Serafine (as f2p u need her for prophecy pool polaris and deathcrawler and she is ok for female dojo if you have good tanks)
Heroes you want to lucksack from COF or Diamond chest: GORAM, SYLPHI, orkon... malrath... and then NOTHING.
My advice to being completely f2p would be to not play this game... The 3 buck dia subscription is really one of the best deals in this game you will ever get. Once you are level 50 you can buy ezio, rayman and prince of persia for a buck each.
The 1st time you buy the diamond chest subscription it is 10 dollar for 40 tickets, that is also a great deal.
And batman for 10 bucks is kinda expensive but he is completely overpowered and the best hero in the game :p
Few tips: you can reset cof by leaving the fight. It will reset everything to BEFORE you entered your fight, NEVER buy single diamond chests only buy them x10 and even then they are pretty bad investment as you only want goram and sylphi really. Set ego aside.. if people beat you in pvp never buy resets etc. Try your hardest to stay as high as you can but dont waste a single diamond. Do 2 daily stamina buys to make sure you hit 100 asap.