You'll miss no story companions. They appear after progressing through the story anyway. You'll have to make them somewhat stronger through giving them gifts or through talking to them, though. Each one has a different agenda/belief system, so your replies during dialogs can have a different effect on what they believe is the right thing.
Each class has its own companions. Only very much later (in KOTFE) you can get companions from the other faction, but you won't have a story with them, you.
You'll have restricted storage room, but you can buy that either via "Cartel Coins" - the "real money" currency - or via Credits - which is the in-game currency you can earn by doing dailies.
Crafting abilities are 3, of which you'll choose to have 2 active as F2P. You can buy the 3rd with Cartel Coins. Personally, I usually switch off the crafting mission ability, but not the crafting collecting ability, and not the actural crafting ability. You'll need mission ability as well, because collecting and mission gives you mats. You can do a second char, though, which has the mission ability switched on, but anothe one off, for example.
What's imho quite disturbing is that you can send only 1 item per mail as F2P, but The Fleet has a Legacy Bank in which you can story mats et. al. for all of your chars, faction restricted. There are planets which have access to both factions, but i don't remember whether they have public available Legacy Banks there, too.
As F2P you'll earn less that when being a paying player, but it is doable, imho.
The only thing which dives me nuts even today is the ability to not show the helmet, for example, or other clothes, only the standard clothes your character constantly wars because of stats in them are shown - in general character customizations. These must - I think - be bought entirely via Cartel Coins, apart from the race specific ones which are free. There are paid race specific ones, too.
I think the Life Day Event is a good time to start because everything is a bit lighter in mood, then. People are throwing snowballs at each other (and at NPCs)
You can get rewards by randomly "finding" "parcels" by hitting characters (even holograms sometimes !)
The ability to throw snowballs must be bought from the Life Day vendor at the fleet. You can also buy a snowball cannon with Cartel Coins (filed under "toys").
I have no idea about steam, though. I can't help you there. As far as it appears to me, you won't need a separate EA account, but I have never used steam with this game, so I really don't know.
If you start, and the Strongholds are still there for cheap (special vendor on the Fleet), then get one ASAP. During the anniversary each year they cost only 3 Credits, if I recall this correctly, but I don't remember how it is now.
And, choose your server wisely. I have a lone character on another sever, but I don't remember which one was that anymore.
The imperial faction is sometimes the most ... uneasy and aggressive one in the general chat, it seemed to me. I've read really disgusting troll posts there.
This doesn't mean that there are no good people there,. It's just so that teenagers who want to play evul rather play there.
Elitists exist as well, like in every game. They are only noticeable in group content, though.
Be aware of ninja invitations to anything.
After getting through your "origin" planet story, you'll be able to get to your capital planet - faction restricted - but from there you can get to THe Fleet even without having you own ship. You can't get to other planets from The Fleet without having your own ship, though. You'll get your ship after finishing the capital planet story.
As long as you *clearly* communicate that you are new, people will be friendly to you and give you tons of advice.
