im no sifu, but from my experience:

1. Yes. the main cause is probably road vibration. that nut on handlepost clamp always need re-tightening after some time. we can notice this when try to lock and unlock the clamp. if the clamp feels a bit loose, it's time to turn that nut anticlockwise a little. my dahon do suffer this minor issue.

2. yes. probably caused by the frame flex, and over tightened case.

3. no idea. but i guess it should be ok. all i know is that it should be greased. 

I dont think we need to dismantle everything just to clean the chain. Some people dismantle the chain. Some just remove the rear wheel and use chain hanger. Some use the chain cleaner tool. Some just wax their chain like mr kenc.

For me, if i rajin, i took off the the rear wheel, put on a chain hanger, and use the chain cleaning tools. If i malas, i just let it be, spray all purpose cleaner, and use tootbrush to clean the pulley and the chain. Done!

i am no sifu
but changing to hollowtech crank does make a different. how much the different?depends on ur budget.

lighter?the lighter ur bike setup, the more lighter ur wallet i can say

performance does improve. but there also a good perfomance square taper bb that feels like hollowtech (price like a new hollowtech crank) if u insist on staying on the current crank.

Yes.

you'll definitely notice the effect of the reduced weight on your bike's rolling parts. if you put ceramic bb, i think the litepro's crankset is probably lighter than the stock 105 crankset. Just don't lose the crank nut, otherwise u'll get headache trying to get the replacement parts

btw, both of my fb i installed litepro's crankset. but somehow the diameter of the crank nut is different. one is M18, and the other one seems to have even smaller diameter.

"Not attractive" is the most ligit reason for changing your Crankset. Others are just excuses… LOL. While you are at it, might as well change to a correct chainring teeth number for your fitness level.
I swear by my ancestors' graves I change my Crankset because they are ugly.

Tiagra largest i think is 52-36. Litepro 53-39. Single chainring of coz got larger. And im guessing is both of litepro's single or double chainrings are using the same crankarm. Durability, hard to beat a Shimano.

The challenge with your setting is, is the chainring going to be compatible with your chain?

11-36 is already in the long cage category.

llitepro's chainring are for 9/10 speed. if u say your 9 speed chain works on on your 8 speed components, then probably it should works too on your future chainring. i've got bad experience mixing those components before. but maybe mine was the case from 8 to 10 speed. so compatibility issue did arise.

Chainring is not no concern with what speed chain. It's the Front derailleur that you need to be careful.

You did not kill your hub. You degreased and washed off the lube in your hub…
Look up YouTube for tutorial showing you how to lube your hub...

Bicycle are ultra robust… 100years of existence has its strength.

if u plan to used single chainring,
better buy single with chainguard. litepro got it, and ur chain will not drop easily.

if ur planning on using double chainring crank, just dont remove the small chainring coz it would be handy sometimes. u never know when u gonna face the toughest hill. besides, u can manually change from bigger chainring to small chainring anytime with dirty hand i used it last time bcoz no money to install fd.

if u buy the double chainring crank and still need to remove the chainring, u need to find the correct length of bolts to fix that single chainring. there is another way u can used spacers without to change any bolts also.

as for wheelset, the litepro kfun is a good wheelset, 24mm rim profile. its better than ur stock vittese since using sealed bearings.and the rear hub if im not mistaken is identical or should i say oem of novatech hub. novatech hub got so many spareparts.

other than that, u can scout for ruitto wheelset. the low profile 24mm one and sealed bearings. its on par with litepro, also the spoke is nice.but its hard to find locally unless in taobao.

another brand is onka. 30mm wheelprofile with smooth rolling sealed beaeings feel than the litepro,but i saw nowdays also very hard to find.

i hope i answer all of ur question coz im no sifu, just share my expirience.

Lite pro is just another glorified chap ayam… cantik punya chap ayam… if you really serious about Crankset , get shimano, SRAM, campagnolo, FSA, or even LTWoo…

i"ll vote for RT. smooth rolling, lightweight, and reasonable price (taobao).
k-fun is lighter than dahon stock wheelset, rolling also ok lah. produce tame sound.
onka is still available at one LBS here in melaka (406, 74-100mm). New old stock. price oso cheap. hi-profile, aero spoke. but the downside is it's quite heavy too (1.7 kg without the skewer).

yes. that's an Onka. yes, much cheaper than k fun. am not too sure what's the weight of the original dahon wheelset, but for onka's 1.8kg (incl skewer), it's a bit heavy for me. not that i can't cycle with that load, but i prefer to conserve my energy so that i can ride longer distance in a shorter amount of time. btw, the hub is silent type.

i oso am never a user of taobao (same prob like yours). my friend help me to get those items from that website.

if u prefer the k-fun wheelset, no need to order from taobao ler. got one local seller selling it for rm420 (almost similar to taobao price edi). i bought from him last time. too eager to get the wheelset that time that i can't hold my patience to wait for the longer delivery by taobao.

Tcb2010 ask for owner review, not where to buy.