ok im not an expert at this so i'll do the best i can to answer most of you questions.
(i numbered them the way u did)
1) i dont really understand what you mean by being able to upload something without getting hosting, a register, typically, will give u the name and the ability to use that name with a webhost, whether you are hosting it or someone else is it shouldnt matter. Most registers however will automaticly create a page on the domain name you register as soon as you buy it, (usally saying someone bought it from them and it will be here soon) this page is replaced by your website as soon as the domain names foward, which takes about 2-5 days (after you tell it what name servers to foward it to)
2) Ok i also dont understand how you can use a domain name without fowarding it, firstoff domain fowarding is free and comes with your domain name, i also believe you can change the address it fowards to an infinate amount of times. how they set it to your webspace.....well when you got hosting you should have gotten 'Name Servers ' or ips u can use. the Name Servers i believe are an address, the registering company fowards the name of your web address (ie yourdomain.com) to the hosting company's name servers. this process takes a few days because it has to "propigate" to all of the registering companies (it changes the information on a whois search for a domain).... to make a long story short, you put in the panel that your registering service gives you the "name servers" of your web hosting account, the rest is automated and within a few days your name is applied to the webhosting account!
3) many registers let you just buy a domain name-the hosting is usally encouraged by them but is alot of the times optional. for instance i use omnis for my domain name but mthoodhosting for my hosting.
4) ok when you transfer a domain name its between registers, but you can often transfer it from a register to hosting if the new hosting has their own registering service. cost is dependand on who you are transfering from and to, it is completly up to those companies
5) why some registers charge more than others? who knows, i believe they charge what they think people will pay, thats all. but some registers offer more options with your account i believe, hence more $$. i typicly go with a cheepest register, especially if you have heared good things about them - but that is 100% a matter of opinion, and everyone will tell you something different
6) this one im not sure about, my hosting gives me my emails and subdomains but im not sure about other registers and hosts, again i believe it probably depends on who you get it from
7) i wouldn't register my domain with my host. i have heard horror stories of people who try to leave their host and are stuck paying huge fees to transfer the domain as well
8) best domain register. my opinion there isn't one, somewhere somehow someone will love and someone will hate a register, its part luck and part figuring out how many more good stories are their over horror stories with a register
i hope this helps, and i hope all the info is correct, if not im incredibly sorry and im sure someone else will correct me anyhow