Hi Mahmood,

1. From the top of my head: 1 TTL load is 400 µA.

2. They are not necessary, but it may be advisable to place them. If your circuit is going to be in an electrically noisy environment, I would certainly add extra pull-ups.

3. A common value is 10 kOhm. Again, they are not necessary for ports that have internal pull-ups, but they can help 'immunising' your circuit from noise.

4. I don't think the position of the pull-up matters much. I usually place them next to the controller. Those nice SIP networks are great for this purpose.

Best regards,
Rob Klein.