I've driven many F30's so I will throw in my 2 cents for whatever its worth
First the only thing I can absolutely say is a must have is the lighting package....it just loses the BMW look without it and I hear there is no true upgrade available after the fact
Second, if you had unlimited funds you probably would not be posting this thread, therefore anything after that is all personal opinion.
I use my nav and iphone alot so the navigation for me was essential and comes with everything you need, tech package is really not important unless you want a Head Up Display which I did not and still do not like, I remember when corvettes had it ages ago and I hated it then and still do now although BMW did a much nicer job with it.
Forget all these tech upgrade with all these cameras...totally lame, buy a lexus if thats what you are looking for.
The handling package and sport automatic tranny are cool if you have spare money but you def do not "need them" as you would drive the car in a way so much where you will see that a vast difference. All the sport auto gives you is a nice appearence and paddle shifters, Drive sport mode comes with the regular auto tranny so no loss.
I personally loathe sun roofs but its totally personal I live where its warm for 3 months and ive never used em in the past....maybe if i smoked or wanted the extra weight or wanted to fix it in the future or liked the wind noise it makes or like the sun glaring on my shaved head then i would get it
You would be happy with the leather and lumbar support and comfort access but it's an expensive option so its not neccessary, leatherette wears better especially if you have kids
Cold weather package is cool but like i said if you are on a budget just get heated front seats its really the most important part
Save money on paint it you are looking for black or white dont get the metal flakes....nothing looks better than a freshly waxed Jet Black BMW!
As far as sound system no need for harmon kardon TRUST me on that one the stock sound system is amazing...ive heard both and cant really tell much a difference at all
I would however reccomend you get a line of your choosing, I like the sport or m sport line but thats just me, I think you would regret going without one
Usually on these forums it's people rattling off what they got on theirs but it truly is all about personal tastes, let me know if you have questions