From a lesson here, I don´t suppose where the questions come from is important. I am mainly concerned about checking my answers. Also I had additional suffix and grammar questions after these, which tie in with my responses, if I may ask.

Q. Emre biriktirdi paralarda ne yaptı?

Emre uzun yıllar çok çalıştı.

Q.Emre en çok kiminle konuşuyor?

Emre arabasıla en çok konuşuyor.

Q.Emre ne zaman arabayı yavaş kullanıyor?

Çamurlu yollarda yavaş kullandı.

Q.Emre otomobile neden hiç kimseyi almıyor?

Çünkü Emre ‘nin arkadaşı arabada çamurlu ayakkıbılar kullandı.

Q.Emre’nin neden çok arkadaşı yok?

Çünkü Emre belki sadece arabası hakkında sevdi.

Q.Emre geceleri neden uyanıyor?

Çünkü Emre arabası çok sevdi.

Q. Sizce Emre nasıl bir kişi?

Emre arabası hakkında çok endişlen.

1. ·         Proper use of -le/-la suffix after a modified noun, or can you use the -ile participle?
2. ·         Describing adjectives such as slowly, muddy, highly, etc, do you use the -lı, -li, -lu,-lü suffix for any of them?
3. ·         Which is the best way to use "worried" as in to say "she is worried about the storm"   Endişlen, kaygılan or üzül..or something else?

1. There is no strict rule about when to use -le/-la or ile but avoid using -le/-la with proper names and especially with abbreviations such as ABD, NATO, EU etc. when writing. For example, "Türkiye ile ABD" looks better (to me) than "Türkiye´yle ABD", and "ABD ile Türkiye" than "ABD´yle Türkiye". 
2. slow is adj/adv. (yavaş and slowly is adv.(yavaş yavaş or ağır ağır)(yaya yolundan yukarı ağır ağır yürüdü= he walked slowly up the path) / mud is noun (çamur) and muddy is adj.(çamurlu) (muddy shoes=çamurlu ayakkabılar) / highly is adv. (son derecede eğlendirici bir film =a highly amusing film)
3. Worried means endişeli, kaygılı and "She is worried about the storm" means "fırtınadan endişeli", but we prefer to say "fırtınadan korkuyor" which means "she is scared of the storm" 

Thank you scalpel, for the good inform about the suffixes, and adjective/adverbs.

It should be noted that I did not write those question senteces, I only answered them. That is how they are in the lesson. I am not sure if one other question was actually covered in the paragraphs, like number 5, and didnt understand quite what it was asking so my answer was a guess.

Emre´nin neden çok arkadaşı yok? 

İs this asking "why doesnt Emre have many friends?" Lastly, I had thought the ıdea was to keep the tense the same as in the lesson, which was past tense. So I wrote the past tense form of the verbs.