brake fluid have to be dot 4 ???

DOT 4 has a higher boiling temp than DOT3, which means it will withstand higher brake temperatures. 4 is also less likely to attracting moisture - more important to cars that aren't used for extended periods. It also costs a bit more so if you're a driver who is not too hard on the brakes and drives fairly easy, 3 might be sufficient.

Yes, there is a specific procedure and sequence to bleeding your brakes. Most Hanynes manuals outline the procedure for specific models well.

The model is important since the technique varies.

I am most familiar with the 1800 since I just did mine this summer. There are 6 bleed nipples (2 ea front calipers and 1 ea rear) that need to be done in a specific order to keep things happy. Plus, you have to dis-engage the brake proportion warning switch so is does not get damaged during the process.

Your model may be simpler but do the research first.