1) I assume you mean percentage of CPU and RAM used? This is dependant on what you are doing with the computer at the time. The CPU will normally register some use (a few percent) when the computer is doing "nothing" due to background processes. It could go to 100% when doing something intensive, for example encoding a video. Memory use is dependant on how many programs and processes are open at the same time. Unexplained high CPU or memory use can be caused by a problem with a particular program or process. Using Resource Monitor can help to pin down what process is using CPU, memory or accessing the disk.
2) Yes having a lot of programs open at the same time, particularly large programs like video editing suites, will cause CPU and memory use to increase. Using less programs at the same time will improve system performance. Is there any need for using six anti-malware programs at the same time?? Using more than one real time virus scanner can cause problems as they can interfere with each other.
Virtual memory is not the same as physical memory. It is when data in the physical memory is moved to the hard disk to free up your physical memory to do something else. Accessing virtual memory is many times slower than accessing physical memory, so it's not ideal to have programs running in virtual memory as everything will get very slow.... You don't say how much memory you have but if you are regularly getting high memory use, then buying more seems a logical step. Be aware that 32 bit operating systems can normally only address 4Gb or less. 64 bit OS's don't have this limitation.