Ouch that's a lot of latency when it comes to typing. This is usually caused by CPU utilization at around 100% and most of your RAM being used up.
That's a tight budget you have but luckily one quick search for $425 laptops lead to a pretty solid contender for your needs - Acer Aspire 3
As for your questions I will answer to the best of my ability:
A.) Adding more RAM will speed up your system but this depends on how much RAM is being used. If 3.5gb is being utilized out of 4gb of RAM, then yes, adding up to 6gb of memory will increase your system's performance. However, using the same scenario, if you increased it to 8gb instead of 6gb, the performance increase is relatively the same. (Assuming the memory usage is still at 3.5gb). More memory means you can have more applications open simultaneously without taking a performance hit.
Do not forget that the parts of computer system work together. Even if you have 16gb of RAM and your system still isn't performing well, the next issue, (though this typically depends on your current operation), could be that your CPU is working harder than it's intended. Low clock speed and a low number of cores can cause issues with processing. This includes the processing that happens when you hit a key on a keyboard and it comes up on the monitor. If you want more info on this, don't hesitate to ask us.
B.) If you're asking if a SSD is better than a HDD, that would again depend on how you intend use it. A SSD is faster (better) for file operations such as loading applications and boot times. You generally only ever see the benefit of a SSD when you open an application. A SSD shines when you use it for booting up your system.
In your case, I believe 6-8gb of RAM is sufficient for what you do on your laptop, as well as a CPU with a clock speed of at least 2.5ghz and at minimum dual cores. A SSD is of course entirely personal preference.
Disclaimer: For those of you hardware junkies that know much more I am 100% aware that I'm not explaining in detail what these pieces of hardware do nor to their full potential. That is intended so that OP can obtain a high level understanding which is more important than the low level details.
That's a tight budget you have but luckily one quick search for $425 laptops lead to a pretty solid contender for your needs - Acer Aspire 3
As for your questions I will answer to the best of my ability:
A.) Adding more RAM will speed up your system but this depends on how much RAM is being used. If 3.5gb is being utilized out of 4gb of RAM, then yes, adding up to 6gb of memory will increase your system's performance. However, using the same scenario, if you increased it to 8gb instead of 6gb, the performance increase is relatively the same. (Assuming the memory usage is still at 3.5gb). More memory means you can have more applications open simultaneously without taking a performance hit.
Do not forget that the parts of computer system work together. Even if you have 16gb of RAM and your system still isn't performing well, the next issue, (though this typically depends on your current operation), could be that your CPU is working harder than it's intended. Low clock speed and a low number of cores can cause issues with processing. This includes the processing that happens when you hit a key on a keyboard and it comes up on the monitor. If you want more info on this, don't hesitate to ask us.
B.) If you're asking if a SSD is better than a HDD, that would again depend on how you intend use it. A SSD is faster (better) for file operations such as loading applications and boot times. You generally only ever see the benefit of a SSD when you open an application. A SSD shines when you use it for booting up your system.
In your case, I believe 6-8gb of RAM is sufficient for what you do on your laptop, as well as a CPU with a clock speed of at least 2.5ghz and at minimum dual cores. A SSD is of course entirely personal preference.
Disclaimer: For those of you hardware junkies that know much more I am 100% aware that I'm not explaining in detail what these pieces of hardware do nor to their full potential. That is intended so that OP can obtain a high level understanding which is more important than the low level details.