I not sure if this fits more into one of the " question section" what I understand they are going with a MTG / Pokémon / Yu-Gi-Oh! type of experience . So collection will matter In illuvium Arena to a point. but the basic Idea is
Illuvium Overworld &Arena - the main PC/Mac game = no mobile / no land
Illuvium: Overworld is built as a Single Player game like Witcher Mass effect Dragon Age ( personally i think that is awesome myself ) With 2 PVP arenas which are the only place you will see other players when the game launches.
Everyone starts out in the T0 area FTP area with 0 Illuvials but if you want to progress in the game you will need build a team of T0 illuvials and then to travel to the T1-T5 areas which have recurring travel and equipment costs its been said the economics is going to be more of a MTG/Pokémon trading card experience.
Its been said Every time you interact with T-1 -T5 areas ( with varying prices depending on rarity) there will be both fuel and equipment costs it been said a run could take apox 1 hour. So if you wanted to do 10 runs in T1-T5 area, you would have pay 10x fuel & equipment cost just like you would have to pay for 10 packs of cards
However None of the specific economic on pricing it self, times or anything else has been officially stated
So we can theorize the barrier of entry will be similar to that of new people starting one of the games mentioned above today compared to the people playing since day 1.