I played everquest for approx 4 years POP through Dragons of Norrath. As far as characters are concerned, are my previous characters; Knight Elf, Froglok, Vah Shir going to be locked as a free player or as a previous subscriber will they be accessible?
They'd be accessible. Doesn't cost you a dime to log in and check, either. Any characters that were created prior to the f2p program are grandfathered and can be played regardless of race/class. Now some of the gear/augs on them might be disabled due to the prestige tag, but that's a different question.
If you find your characters unplayable due to the prestige tag restriction, you can always /testcopy and play on Test. On Test, your account is unrestricted, and we have a reasonable player-base now, making it more like a Live server in terms of numbers.
You're not going to run into any issues that are going to keep you from being able to play. The only items that you are going to run into that your character owns currently that might have the Prestige tag are going to be augments (gear does not start having Prestige tags until Tier 4/5 of SoD and the final 1-2 tiers of subsequent expansions). You won't have to do anything; the gear you have will simply not benefit from the aug's stats. These will have the background shaded purple when equipped. If the background is shaded Yellow you are generally too low of a level to wear the equipment (a change made to address the issue of respawning fully equipped and losing a level. Also all of the quested augments listed in the Hero's Journey Achievements as well as some special event augments (Anniversary & Holidays), the Defiant Augments (random drops of old quality gear at all levels), and Hot Zone augs (hot zones are zones with their Zone Experience Modifiers temporarily punched up to PC levels, these zones also have special drops in them) are not flagged as Prestige so you will be able to use those.
How about cash? If i had a couple million PP 3 years ago, and left the game, if i log in free2play, does all that cash vanish like Michael Jackson hearing sirens at Chucky Cheese?
It could be locked, or even vanished, you could try to petition once you go back to gold account status to try and get your plat back.
