Well, thats rather from case to case. Some people from Serbia would say, Kajkavian sound to them Kajkavian sound more like Slovene. But, I dont think we could classify South Moravian dialects as Bulgarian or Macedonian. For start they have declension, which is completly analytical. Rather South Moravian dialects are transitional forms between Bulgarian and Macedonian dialects and Štokavian dialect.

Well, that is more about being exposed to media. Serbs generaly could understand Croatian standard pretty well, even today. (It has lot to do with HRT, RTL, NOVA etc on Serbian cable providers). I think biggest difference today is in acadmic literature, since Croatian and Serbian scientists on unversities are using different nomenclature, and there is no way to that two to converge. For example I could speak about theolgogical dictionary. Even when translating same books from Greek and Latin, Serbs and Croats use verry different terms, different roots, suffixes, afixes etc. Same thing you could trace in phsics, chemistry, philosophy (bitak-suština for example).

Well in Serbian there is difference between što and šta (relative and asking pronoun). Also, there is difference between čorba (broth) and supa (soup). What croats use for broth (boulion)? I know supa is juha.

Moji susjedi jedu komad kruha. Moji komšije jedu parče hleba.
Tjedna događanja. Nedeljna dešavanja.
Doslovno u rekli da će temperatura zraka ovog tjedna biti oko 20 stupnjeva. Bukvalno su rekli da će temperatura vazduha ove sedmice da bude oko 20 stepeni.

Doslovno, komad etc are common in standard Serbian. They are even more likely to be heard or written
than bukvalno or parče (there is even slight difference between parče and komad, komad having wider meaning). Also, bukvalno could be pretty offten hear don Croatian TV.

Well, komad, deo, dio, zrak, štednja …. those all exist in standard and everyday Serbian. Same thing could be noted about ijekavian, which is part of Serbian standard, while Croats dont use proper ijekavian, not even in Standard Croatian (i mean, did you ever heard somebody saying: “dijete”, I Emphasise dijete, not djete, with long e after j)  Parče is rather localism, accepted in standard, you will never hear: Srbi su parče slovenske porodice, or: Ukroćena goropad je pozorišno parče.

Well, its more about watching Serbian media than anyhing else. Generaly some Macedonians speak Serbian verry good, some have dificulcies. Even those studing in Belgrade.

Ja ću raditi. Radit ću.
Ja ću da radim. Radiću.
and use of infinitive whereas Serbian rarely uses it. Example with modal verb:
Trebam ići u grad. Moram napisati.
Treba da idem u grad. Moram da napišem.

While Serbian rarely use infintive, ase consequence of being exposed to Blakanic sprachebund, trebati is bad example. Verb trebati is impersonal in Serbian grammar, which means its never conjugated. And it is not modal verb in Serbian also. Serbian modal verbs are: morati and moći. Anyway, if somebody would use moram napisati, he would not be misunderstood in Serbian. It could sound bit archaic to some speakers, but it will never raise doubts hat speaker wanted to say. 

So Turbo-folk is some reper of Ottoman cultural influence? I dont think so. I saw literaly hundreds and thousands of young Slovenes who adore such kind of music. No need to remind you it has nothign with Ottomans. (Affinity to to some music).
Anyway, Serbian and Croatian cultural difference predate Ottomans and turbo-folk for centuries. It has much more to do with kind fo Christianity two peoples converted into. Serbs accepted Orthodoxy, hence more Helenisms (especialy in phorm of vitacism), Russism, Church Slavonisms etc. Croats accepted Roman Catholicism, thats why more Czech, German, Latin and Italian  borrowings.
Apropo Central European/Mediterannean culture its oxymoron. There is  no such culture. Of course Croatian culture has influences from both. And in some part one is stronger, in some parts other.

Well Štokavian and Čakavian are held to seam from same source. And Serbian is not classified as South-eastern Slavic language as far as I know.

And Kajkavski and Čakavskiare closer to each othern than both to Štokavski.

You could compare text between three.
And Standard Croatian is mixture of all 3 of them with Štokavski syntax as basis (which means that Kajkavski ‘tjeden’ becomes ‘tjedan’ for purpose of Standard)

Its not mater of syntax. (I mean your example), syntax is branch which sets rules for making of sentences. What you showed is shift from alternation of e to alternation of E