Question: If I were to buy a $29.99 3-month Xbox Live Gold card from the Doylestown, PA...

I'm from PA (originally from Philly-moved to Doylestown). I live in Ireland now, but more friends are welcome.

and please do you roccemend buying codes online from websites such as
www.pcgamesupply.com/.../Xbox-Live-3-Month-Gold-Card-Code or from retails ?

It depends on when you're adding it.

If you do not already have Ultimate, you add the Gold card, then buy Ultimate, you'll get the full 3 months.

If you already have Ultimate and you add the Gold card to that, you'll get 50 days of Ultimate.

Can't use a gift card to buy Xbox Live Gold. You must use a credit or debit card or funds from a PayPal account to do so. In addition you can buy a 1 month or 3 month or 1 year Xbox Live subscription card and redeem that via the website or console.

its a green xbox live gold 3 months card so i can't use it to buy games in game purchases???

You can't buy games or in game purchases with a 3 Month Gold membership card.

But even if you have a subscription, you can redeem the card, and the card will "pause" your renewal payments for 3 months, and after the 3 months of the gold card are over, you start paying normally for your subscription again.

So just redeem it on your account, and you save 3 monthly Gold payments. And even if you have a longer subscription (like a 12 month subscription), it will "push back" the next renewal payment for 3 months.

So for example, if your next renewal were in November 2019, and you redeem the 3 Month card, you'd have to pay for the next subscription renewal in February 2020.