1.yes you need to buy the upgrade, eso+ is only for dlc.

2. Imperials passives make it proficient as a tank and stamina dd.

3. So much to tell on this topic, I really do not know what to advice on.

4. No it does not come with eso+, they removed that when it switched to become a dlc, have to buy warden class now. Or if there is a bundle pack that says you get warden if you buy morrowind.

5. Nightblade fit very well as an assassin/thief. Imperial soldier, I would say stamina Templar come closest given their abilities. Since I think of imperials as romans.

@Maxximus

3) On a side note, I'm new and looking to enjoy the game. I'm new to MMOs too so I'm pretty lost. I really don't want to screw up my character at the beginning of the game then end up with a dead character by end game. What should I do and keep my eye out for?

You can reset your skill choices and attributes at any point so you wouldn't end up with a dead character. Changing gear is really easy.

I'd just start questing and see what happens... I was well into the story before I even attempted a dungeon or any other group activities. I actually played a bunch of Cryodil PVP and that was my first group experience.

So Imperials have more Health than other stamina DPS classes which means you will be safer and less likely to die. They also make good tanks.

@Narvuntien Oh you can reset attribute points? That's good to know, now I'm not as stressed hahah

Because others covered the other points already, I will leave the comment on the third one.
You can't screw your character in this game. Even if you will choose wrong race for your playstyle, you can change it through Crown Store.
The thing is, people are overestimating the usefulness of race chosing. As long as your race has bonuses that fits your character build, you can complete EVERY content in the game without issues, including hardest of the hardmodes. Some people are minmaxing characters in every aspect and that's necessary only for end-game progressive raiding for leaderboards, what requires from you to spend around 15 hours every week of raiding with your group. But even if you don't aim for it, and you just feel comfortable having minmaxed character, I will list BiS races for every PvE build here:
Magsorc: Altmer
MagDK: Dunmer
Magblade: Dunmer
Every stamina dd: redguard.
Tank: imperial or Argonian
Healer: breton or Argonian
Magplar and Magden are not competetive dps classess currently, but best race for them would be Dunmer for current patch.
The only race I wouldn't recommend is the Nord, due to weak damage reduction, what is strongly affected by diminishing returns and barely gives something. Also frost resistance is quite terrible aswell, since in this game you can barely meet dangerous frost damage sources. Anyway - as I told it doesn't matter at all, so if you like Nords I would recommend building this character into stamina due to 6% passive max stam increase.

But as long as your character has race that boosts their strength, it's already ok. For stamina oriented class you can pick: Redguard, Orc, Bosmer, Khajit, Imperial
For magicka oriented class: Altmer, Dunmer, Breton, Argonian
If you wanna play PvP, Argonian is insanely strong in every aspect, due to incredible sustain, massive healing bonuses and complete immunity to Disease and Poison status effects.
Hope it helps.

Imperials are also great at crafting, since their racial motif is pretty rare compared to the others,and having it allows you to create imperial outfits as costumes for you characters.