Heya,
Welcome to the game
Answers to your questions are below, but I left some personal insights at the end as well, just in case
The main difference that chromie time makes is that it stretches content out to the full level range of 10-50, rather than each expansion’s zone’s respective level range.
Without chromie time, the zone’s level ranges are as follows:
- Vanilla Zones: 10-30
- Burning Crusade Zones: 10-30
- Wrath of the Lich King Zones: 10-30
- Cataclysm Zones: 30-35*
- Mists of Pandaria Zones: 10-35
- Warlords of Draenor Zones: 10-40
- Legion Zones: 10-45
- Battle for Azeroth Zones: 10-50
As you can see, most zones have an upper limit, beyond which mobs don’t scale anymore without chromie time, so the main difference is that it stretches the mobs beyond the limit to scale up to level 50.
*Keep in mind that scaling does not apply to the lower limit, so even in Chromie time, the 5 separate Cata zones only start scaling from level 30 (although they will be stretched up to level 50)
In regards to what is “better” that’s difficult to answer since chromie and warboards aren’t the same thing. Chromie time doesn’t add or remove content, but just changes scaling. Generally speaking, chromie time makes it easier to prevent expansion hopping, but it sounds like you will freeze exp gains and efficiency isn’t your main goal, so you can choose either one. Chromie time helps in pushing relevant warboard quests of the expansion you selected to your character, and while the system is really confusing, outside of chromie time you have to really know where to pick up breadcrumbs, so it could be difficult to find the right starting quest for each expansion’s storyline.
IMPORTANT: Chormie time becomes unavailable once you reach level 50, as it is mostly a leveling tool. This won’t change much,(since again, Chromie doesn’t remove or add content) but just know that once you dinged 50, chromie time won’t be an option anymore.
That is also mostly up to you. Chronology across expansions isn’t a huge issue in earlier expansions and most of the main storylines are looked at separately (only in the past 3-4 expansions did they weave main storylines together into an overarching narrative).
If you want to go in the correct chronological order, it would be TBC-WOTLK-Cata (including overhauled vanilla zones), but know that you can also go with overhauled vanilla zones first, then TBC-WOTLK-Cata. There might be a few zone quests that could reference small thigs from earlier expansions, but that really shouldn’t be too disruptive or cause you to feel completely lost.
Personal recommendation: Alright, now that we covered this, I want to share my insights as to why I don’t think doing everything on one character is a good idea
Please don’t get me wrong, this is totally your decision, and either way works, but the overhauled leveling process and level squish caused leveling to put you at level 50 much (much) before completing an expansion’s zone and main story quest. This means that even if you stick to one expansion you’ll be done with leveling much sooner than the content of the expansion, so you will spend a lot of time on a single character that isn’t progressing in their power.
It is much more enjoyable to go with one character per expansion. It doesn’t only provide variety for your playstyle and invite you try out different characters and talent builds, but gives you a big roster of leveled characters to pick from at the end (about 7 characters) so you can see which one you like best, and bring that one into the new expansion and latest endgame content.
Most questing achievements for each expansion are account wide, so your account will have questing/exploration achievements and meta-achievements unlocked at the end, even though you do their parts on different characters.
One last point is also related to the level squish. Freezing exp might cause a strange experience, since the level squish caused for your core abilities and passives to be spread out between 10-50. This means, that if you intend to level freeze before level 50 (for the sake of argument, let’s say 30) you might end up with a character with an incomplete moveset/skillset/talent setup, making them feel not rounded to play. The solution to this is just leveling to 50 and then doing all expansions ont hat character at 50, but that brings us to the point above that you’ll spend a lot (like a lot, I can’t stress this enough) of time playing a character without progression/growth in their powerlevel.
Alright, that’s it from me. Again, the choice is totally yours, and you’re offered a good bit of flexibility, I just thought I’d share some insights here as well, since there really isn’t any mechanical advantage to do everything on one character (like other MMOs tend to offer).
Hope that helps, and sorry for the wall of text here
The important thing is: however you choose to play, have fun!