Wow!! Lots of questions! LOL Okay...let's start with this one first. There is soooo much you can do with LauncherPro (LP). For starters: You can create 7 home screens, compared to only 3 with your stock launcher (Canvas). When you first start your phone and click on menu your Desktop will be the first to show up. Click on menu and select 'preferences'. Then select LP Widgets. If you want your weather widget with the clock, select it from the choices in LP. Click on the settings for the widget and format it the way you want it. Go ahead and experiment. You won't hurt it!!! LOL
Also, if you had this running on your stock launcher it is still there and it is still running in the background. This will slow up your performance. The solution to this is to open up Titanium Backup and touch Backup/Restore, then select 'Canvas' ...then 'backup' ....then click Canvas again....click 'Freeze'. You will see that there is an option to restore it whenever you want. This is the easiest way to stop it and it will be there in case you want it back.
LP will give you the option of creating however many screens (up to 7) that you want. When you select 7, then you scroll sideways and a new blank screen will appear. Just long press to add whatever app icons (shortcuts) you want. Do this with each screen. I have my facebook widget on one and on another I have my calendar. I have three screens of apps. If you take a look at the Step by Step Instructions for Rooting thread you will see screenshots I took of my phone with LP . It doesn't look the same now as I had done more customization.
I don't use a task killer. I think when you freeze Canvas it will solve a lot of the probs you are describing.
Try what I suggested above and see if it helps you. Also, be sure to download a good Cache Cleaner: Cache Mate or Cache Cleaner NG
Clearing your cache is really important.
Go into each of the above apps and open. Then click on menu and uncheck 'start automatically' or whatever option it gives you. Look at the other settings and uncheck those that make it come on...eg: sign in automatically (for gtalk). There will be some apps that you see in your running processes that you need for everything to work correctly.
If you feel you need a task killer then keep it until you have everything running more smoothly.
Some apps will cause your programs to 'force close' more often. Try to see which of these apps is causing you probs and get rid of it if it isn't a stock app you need.
Hope this helps. Maybe someone else will come up with more info to help you!!!