This is quite common and pretty harmless. The scratches you see don't go very deep, nor are they very wide. My All-Clad saute pan is nearing 10 years old and has a ton of micro-scratches on the interior. It still performs beautifully.
That said, the scratches can grab onto proteins and cause sticking. However, this is simple to prevent with both oil and proper pan preheating.
When a pan is preheated properly the metal expands, essentially closing all of the micro-scratches. This prevents the proteins from grabbing onto them and getting stuck. You obviously need oil/fat to assist with this as well.
To properly heat a pan to the appropriate temperature I suggest using the water drop method. If you put a cold pan on heat and drip a drop of water onto it, the water will sit there for several seconds then boil away. As the pan gets warmer this will happen more quickly, fizzling away in a second or so. Once the scratches start to close something weird happens.
First, the drop of water will break into a few mini drops which scoot around the pan as they evaporate. This is a sign that you are almost there. When the drop of water stays whole (mostly) and scoots around the pan like a mercury ball, this is the perfect temperature. I the water instantly vaporizes on contact, you've gone way too far and need to let the pan cool down. At this point you should add your oil/fat, swirl it around, and immediately add your food. (Make sure the mercury ball of water is gone before adding oil).
Also note that the mercury-ball phase is definitely too hot for unclarified butter, and may be too hot for some extra-virgin olive oils. They may instantly smoke upon adding.
Again, it's important to have your oil and ingredients in place (mise en place) before you start. It's quite easy to skyrocket past the mercury-ball phase if you have to open your oil, pour, and then season your ingredients.
Enameled cast iron usually means porcelain enamel, a type of glass. It's resistant to both acidic and alkaline foods. It is fine to cook and even store tomato sauces, etc. in enameled cast iron.
Stainless steel is also resistant to acidic foods, but not as much as porcelain enamel. Storing tomato sauce in it may eventually discolor the pot.
Both stainless and enameled iron are perfectly good options for cooking with acids. Whether you need a stainless pan depends on what cooking you're doing. In brief, cast iron has very slow heat response (e.g., you raise or lower the burner, it takes a while for the pan to cool or heat); stainless is much faster. That's a drawback too, iron gives a very nice steady heat, perfect for braising.
Stainless is also almost always lighter. I have a 12 qt stainless stock pot, its several pounds. My enameled iron dutch oven, at less than half the capacity, is closer to 15 lbs.
Best Answer
A non-stick coating is a specific chemical applied to the surface which makes it very hard for food to stick. When people refer to a 'stainless steel pan', that does not imply that it has a non-stick coating, and people would normally understand that to mean a plain stainless steel surface without non-stick coating.
Having said that, for many applications cooks prefer a pan without a non-stick coating. Non-stick coatings can be damaged by excessive heat or the use of metal implements such as spatulas or tongs. Because the food does not stick, it is harder to produce fond, which is the result of the food sticking to the base of the pan and browning. Most things that can be made in a non-stick pan can be made in a non- non-stick pan, possibly with more effort and technique required. Frying eggs is really the situation where a non-stick pan is at its most valuable.
If you are looking for a non-stick pan, you should read the label carefully and (as Stephie said), look for a (usually) dark, non-metallic surface.