Welcome to the forum!
If you are ready to adopt, congratulations! Proper care is really quite simple. I guess I am confused on where you feel inadequate. You've had guinea pigs before, so you have the experience, just provide the following basics and everything will go very well.
1. Proper housing- provide indoor housing that is a minimum of 7.5 square feet. (Reason: you don't want your guinea pig unable to run laps and having to sit in their waste all day). Pet shop cages are too small and too expensive, so it is easy and inexpensive to build a large c&c cage as most on this forum have done. Proper cage size is mandatory and not pampering or spoiling. Bigger is always better because they can move, excercise, explore...you wouldn't want to live life in a bathroom stall. Also you should have room for a minimum of 2 since they are social animals. Bedding is up to you, I personally use fleece liners that I make myself (also a $ saver!). Here's info on suggested material and what not to use for the safety of your pig.
https://www.guineapigcages.com/bedding.htm
2. Proper food- provide them with unlimited quality hay such as Timothy hay (avoid alfalfa for adults), quality pellets (Oxbow or KMS), fresh water, and daily veggies (green leaf lettuce, bell pepper, ect.). Avoid junk food pellets and treats with colored bits and nuts.
3. $ for an exotics vet- it's not if they get sick, but when, and you should have the means to provide them proper care for regular checkups and unforseen illnesses.
4. Time- you should realistically have the time to care for them daily. You know how much waste these little guys make. So time for their daily care (cleaning to avoid unsanitary conditions, feeding, clipping nails, weighing regularly, play & snuggle time). This is also how you can detect issues when they are small and hopefully deal with them before they become huge problems.
All the good intentions and love in the world does not make up for the loss of the basic necessities that keep your guinea pig healthy.
You will do a great job! After all you are ready and willing to learn for the health and well-being of your guinea pigs. Don't be overwhelmed, we are here for you when you are ready to take on the responsibility of adopting again.