Computer upgrade questions (PSU)

I am currently using a Lenovo A70 (Type 0889). It is a small form factor computer. I think the RAM and graphics are not good enough. So I am planning on getting an upgrade for both RAM and graphics card. Since not all graphics cards fit in my case, it is hard to find one that fits. However I managed to find one that suits me. But I realised that my PSU does not have enough wattage for any graphics card, I must upgrade that from a stock 180w to a decent 400w one in order for my graphics card to work. I have a few questions to ask since I know nothing about computer upgrading. Only
answer if you are 100% sure about it. I don't need you to put the source of information, but i want answers that are correct. My computer was bought about 6 months ago and i don't take any risks. This are my pc specs:

Intel Pentium E6600 3.06Ghz
2 GB DDR3 RAM
Windows 7 32-bit
(These are the only specs i am sure about. If you need more, I will try to find it.)

Here are the upgrades I want:

AMD Radeon HD 6570 (Low profile/1GB)
1x 4GB DDR3 RAM or 2x 2GB DDR3 RAM

Here are my questions:

1. Will a 400w damage any of my components (including motherboard, RAM, CPU(65w) and HDD)?
2. What are the high reputation brands for RAM and PSU?
3. If a 400w PSU works, will my CPU overheat/malfunction?
4 Will my fan run at higher RPM due to higher wattage PSU and/or possibly burn up?
5 Any long term problems after the installation of the new PSU?

Again, I would like correct answers since I am only 13 years old and I don't want to ruin my computer.

Thank you for answering!