> 1. How many as such category can I run in a project with 
> HTT (the category URLs during the start of the HTT and in 
> the Scan Rules), without much disturbing the download 
> speed?
Well, as many as you want - the limit is the memory, or the 
upper link limit, which is by default 100,000 links (but it 
can be changed)

> 2. How many multi-URLs HTT project can I run in parallel 
> in a PC without disturbing the download speed?
Humm, it depends on your bandwidth!

> 3. Is it possible to locate an original URL of a 
> particular type of HTML files that are saved 
> as 'maillinkit3e67', 'maillinkit3f624', 'maillinkit04a8' 
> etc. ?
It is written in the html page sources, in html tags 
comments. You can also find the information in hts-
cache/new.txt

> Would this Scan Rule work ?  
> -www1.askme.com/*maillingkit.asp* or something else.

Yes, ot even
-www1.askme.com/mailingkit.asp?vid=*&cid=*&xid=*
or
-www1.askme.com/mailingkit.asp?vid=1234&cid=*
and so on..

> 5. During the download, the HTTP shows 'Links Scanned', 
> Files Updated (with a %) - please explain the terms. Is 
> there any way, how I understand how much download is 
> remaining ?
It is the scan progress of a file. There is NO way to know 
how much time is remaining, or how many links are 
remaining, because you can't know in advance how many linkw 
you'll find the next page.