Margin Trading Questions (Reg T, Scaling in, Deposits)`

I'm researching how to effectively trade on margin and I'm having trouble visualizing some scenarios and I haven't been able to find anything online so any help would be greatly appreciated.

Here are the hypotheticals:

• Scenario 1: Let's say I want to buy \$10,000 of stock ABC at \$100 per share. I have \$6,000 cash so I buy the full \$10k. I meet the Reg T rules because my original equity is 60%. Now a week goes by and the stock price is still \$100 and I want more. Can I buy \$2,000 more to max out the available margin for stock ABC? (I'm not saying this is a good idea, I just want to know how it all works). How does Regulation T work when scaling into positions? This second tax lot is 100% a margin debit so it doesn't fit the Reg T definitions that I've seen but because it's not opening a position does it not need to fit that regulation?
• Scenario 1a: Let's say I open a position of stock ABC with \$1,000 cash where ABC is at \$10 a share. A month later ABC is worth \$12 a share and I want to enter a margined position. My current equity is \$1,200 so I buy \$1,200 worth of ABC. Would this violate Regulation T because my original \$1,000 down is only 45% of the now \$2,200 held ABC?
• Scenario 1b: Let's say I open a position of stock ABC with \$1,000 cash where ABC is at \$10 a share. A month later ABC is worth \$8 a share and I want to enter a margined position. My current equity is \$800 but I buy \$1,000 worth of ABC. Would this violate Regulation T even though my original position open was \$1,000?
• Scenario 2: Let's say I have 2 positions held on margin. Stock ABC has a margin debit of \$1,000 and stock XYZ has a margin debit of \$500. Some time passes and I deposit cash into the account, let's say \$300. How does that apply to those margin debits? Is it even, meaning, now ABC has a debit of \$850 and XYZ has a debit of \$350 [Original Margin Debit - (Cash Deposit / Count of margined securities)]? Or maybe it credits the first balance? ABC was purchased on margin before XYZ was purchased on margin so the \$300 cash deposit credits ABC's \$1,000 margin debit and brings it down to \$700?

These are very specific examples, I know, but I'd hate to make a mistake before I know the boundaries of what margin can and can't do! I appreciate any help

EDIT: Added Scenario 1a and 1b