Greetings,
I picked up a fabulous collection containing everything from both Baldur's Gate and Icewind Dale ( both the first and second installments with all add-ons ) for 10 bucks.
Now, having only played Baldur's Gate 2 shadow of amn around 8 years back - and my memory of that is understandably hazy - I have a few questions:
1) Which series should I start with ? Icewind dale or Baldur's Gate ? I read that they are somewhat different and people who liked Baldur's Gate where somewhat disappointed with Icewind dale, thus does it make sense to first play Icewind dale before Baldur's Gate , to avoid being frustrated ?
2) Which mods ? Since it will be my first playthrough in years, I'd rather not have any deep gameplay changing mods, but rather only necessities to enjoy the game as it was meant to be played with a few tweaks and changes to make it more accessible and perhaps less prone to crash and glitch.
3) I'd like more info on the baldur's gate 1 in baldur's gate 2 graphics mod. How do you install it and how deeply do the ruleset changes affect the original game ? Does it become easier or harder, more fun or less fun ?
4) What do each of the expansions do ? Like, added content or totally different story ? I want to play the games in their correct order and I don't want to accidentially install a expansion that i wasnt meant to install until beating the game or something.
My questions pertain to both Icewind Dale 1+2 and Baldur's Gate 1 + 2.
I know there has been a thread about mods for Baldur's gate but i had some more specific questions so i felt a new thread was a better option.
Thanks in advance!

1) start with BG1. better game as IWD is full of combat and weaker on story (relatively speaking. great game)
2)Refer to my own thread for answers which mods you should install:
http://www.gog.com/en/forum/general/baldur_amp_039_s_gate_mods/_/1
for bg1 i installed bg1tutu for bg2 engine, unfinished business and banter pack
found them here:
http://www.gibberlings3.net/
3)Simple: install full install of bg1 tos, bg2 and throne of bahl.
download the mod. install it and viola :D works without a glitch at least for me.
few changes... tweaks with spells and added content. can't tell whether harder or easier but i got two high level spells which helped me with incredibly hard battles. more fun that's for sure.
4)Expansion for bg1 adds extra content. separate storyline. and rises your exp limit
throne on other hand continues the story of bg2 and wraps the whole saga.
bg1 expansion can be triggered at any time really but you won't be able to do so after i think third act. i do recommend waiting till level 7 for each of your characters.
install all of them at the same time.
don't know about IWD expansion tough.
all answers relate to bg1 and tosc which i finished two days ago.

Thank you a lot both of you.
You posted both at the same time and comparably same level quality of information so I was somewhat conflicted on whom to "Accept" as answer.
I picked FrenziedAU though as he has considerably less Rep, I hope you won't mind.
If anyone has more information about IWD and its expansions , and whether there is mods out for it, it would be appreciated. =)

I'd like to add that BG1 in BG2 engine mod changes the experience significantly- you get BG2's more powerful classes, can specialize in weapons further that the original game allowed, gain new more powerful spells and so on. Of course the graphics are changed (not in all instances for the better). So i would highly recommend playing the first time with just bugfixes, the way it was supposed to be played. Just saying.

Others have already answered your questions relating to BG1 & BG2 quite well, so I won't attempt to do so.
Regarding Icewind Dale 1 (currently playing through exp), I'm not sure whether you should install the two expansions immediately or not due to some bugs I've encountered.
I installed Icewind Dale 1 + Heart of Winter + (free expansion) Trials of the Luremaster which brought my game up to 1.42 (the latest).
I went through all of Icewind Dale and encountered (spoiler?) the last fight. Unfortunately it was bugged and I could not complete it. I did some light research and found that others had the same result if they had version 1.42. In the end I had to cheat to complete the original campaign. Not very satisfying to say the least.
Then on to Heart of Winter. The neat thing here is that like Tales of the Sword Coast (exp for Baldur's Gate 1 mentioned earlier in this thread), you can start the additional content (Trials of the Luremaster) very soon after starting Heart of Winter, or you can wait a while. Eventually you'll lose the option of starting TotLM, so I wouldn't wait too long.
Long story short, TotLM was bugged for me too. Without spoiling too much, there are four places you have to visit to eventually claim something you'll need to go forward. Two of those places I couldn't enter which left me effectively blocked from going forward.
Thankfully I found Dale Keeper and was able to give myself what I needed to continue.
Lame. VERY lame.
Since Heart of Winter gives you the option of importing your previous party from the original campaign (and I did so), I could have very well brought more problems by doing this instead of creating a new party and forcing them to a similar level through cheats.
Long story short, weigh carefully whether you want to beat the original campaign without Heart of Winter + Trails of the Luremaster installed.
You could install Icewind Dale 1 + the 1.06 patch and beat the game, then install Heart of Winter and Trials of the Luremaster and import your characters.
On a slightly different topic, Icewind Dale 2 doesn't have an expansion that I know of, nor does it import your characters from IWD1. I believe it is set much later than IWD, so that would explain why importing isn't an option. I don't think IWD2 has any patches for it, so I dunno if there are any bugs (haven't played it yet).
I hope that long bit of rambling helps answer any questions you have. Here's hoping you don't run across any of the bugs I did!

You can't import your character from IWD to IWD2, because it has different ruleset (IWD fisrt ADnD, IWD2 third ADnD).

That certainly makes technical sense, but I imagine a good reasoning for not wanting to go through the hassle of supporting an import option would also be the setting is so much later. :P