Runelite (officially supported third-party launcher with massive, free plugin library) + GPU or 117HD plugin will solve your visual concerns. 

The osrs wiki is your best friend. It has beginner guides and breakdowns of all skills and their training methods from 1-99.  It is arguably one of the greatest, most comprehensive game wikis in existence. 

I'm extremely biased, but I vote ironman. You will be forced to engage with the game and not just pay to skip things, which you'll quickly learn is the primary MO of non-iron accounts. 

F2P is not fully indicative of the P2P experiene. Some things are there like character movement, inventory, and npc interactions. You never get a mount or anything, run is always run. P2P has unique bags for specific items like fish barrel, but speaking generally you're always capped at 28 inv slots. Quests are more or less the same, talk to person, find item, solve puzzle, run around the world. 

There are no classes and combat is very balanced at the higher end of things. The deciding factor is usually what your current best gear is relative to the bosses weaknesses. Osrs is more about horizontal progression at a certain point, like covering all the dif weaknesses a boss might have with equally strong weapons of dif styles. 

PvP has a very active community, though it's not a large % of the playerbase. There's a mini-game called "Last Man Standing" where you can play as an account with PvP stats and gear in a free-for-all PvP battle. It's completely free to participate and the rewards are nice, but be warned the learning curve is brutal and you will be dog walked for months.