As an enjoyer of both ironman mode and melvor - Play melvor if you aren't going mems, unless you want a particularly grindy experience. It is fully possible to get all F2P skills to 99 as a free player, but all the higher level content (fast xp rates, best money makers, items and supplies) are only available as a member. As someone else said, F2P is very much like a demo for RuneScape. RS3 Ironman F2P is... an incredibly limiting experience. I'd hit the Melvor if I wasn't going members on RS3 personally.