WOW..lol ok Bluepup lets see if we can answer some of these for you..
1) Which connection type (i.e., primary or secondary) enhances and which decreases probabilities of successful file exchanges?
Basically this depends really on the user and the machine they are using as well. There is no clear cut answer to this, I will say this. A well configured secondary connection can work just as well and in some cases better then a primary one. On primary your supporting network traffic as you know (i see from next question) this can cause alot of resources to be used and for some machines this can cause primary to work very poorly. Using a secondary connection that has ports, firewalls, routers, modems etc.. all configured with ports to allow WinMX to work can be much better for those users (like myself included) that find primary lags or uses too many resources.
Bottom line.. get things configured correctly and try both to see whats best for you.
2) Generally, do users with primary connections look down their noses at users with secondary connections?
No generally Primary users are glad to see secondary users because the idea of them using primary is to help the network and support other users on secondary enjoying WinMX also.
3) When users have fast Internet connections, what is the purpose of limiting numbers of downloads and uploads?
WinMX can be a hungry beast especially on primary, if there are no limits set it can use all your available bandwidth. The long and short of this is that with limits set on Outgoing bandwidth this leaves a better balance for bandwidth shared not only between downloads and uploads but between WinMX and other things you may require bandwidth for your doing on your PC. Having Upload Slots set to one on highspeed is a bit excessive if you dont have any monthly limits on bandwidth from your Internet Provider 6 is the normal upload slot default set by WinMX, I personally run 3 slots and the reason is that those three users get more bandwidth and finish files faster then if i shared my bandwidth between 6 users. Therefore the files finish faster and the next three in line get to finish files ..etc...
Most home users do NOT have a T3 line and if you read those things its usually not true.. some ppl mistakenly think that setting that in Settings > Internet Connection will increase some speeds, that setting has no effect on speeds.
As for the Queueing that is often a side effect of programs such and MxMoni which can ignore users by the number of files they que up, most ppl using that will allow three files at one time, Im not a big fan of this feature of that program but its not a WinMX feature so its not going to be happening with all users.
4) Comment: ALL would benefit from specific instructions suggesting appropriate settings for their systems, in that many users appear willing, but are unable to configure to allow file sharing.
You may not have noticed we do have a extensive tutorial section with help on most specific issues, the fact that there are so many set ups out there, high speeds, dial up, routers, modems, etc its best to learn about the settings. WinMX is very versatile program, one of the things I love about it and there fore your set up is geared towards what works best for you.
Hope this help you some and here are a few relative links to the above ..https://www.winmxorld.com/tutorials/helping_winmx.htmlhttps://www.winmxorld.com/tutorials/winmx_basics.htmlhttps://www.winmxorld.com/scripts/bandwidth/
These are just a few located here:https://www.winmxorld.com/tutorials/winmx_index.html
Hope this helps you and if I've created more questions then just post back.. LOL