Something to keep in mind is that Poland suffered terribly during World War II, both from the Nazi conquest and occupation and the Russians re-conquering the country. There were numerous wars prior to that. The partitions of Poland had their effect as well.
The archives you are using should give you an idea of how far back records exist. If your family was part of the main religious group, the chance of older records existing is higher. If the family was Jewish, much was purposely destroyed, and finding earlier records becomes difficult to impossible.
Depending on where in the country, and when, you need to have some familiarity with Polish, Russian, German, and possibly Latin. It is fairly easy to find genealogical word lists, which is a start. Looking at transcribed and translated records can be very instructive in understanding how the records are laid out. You can learn how to pick out the essential information.
Learning the handwriting is important. It does take some work. There are some online sources that can help.
To your question, how far back can you go? Short answer: it depends. Catholic records formally begin in the mid-1500s with direction from the Pope. The reality, however, actual start times vary all over, and very early registers are rare.
I have some British baptismal records from about 1810; but the names are so common, with so little specifics, going back earlier isn’t at all likely.
In France, the French Revolution can be a difficult event to get past. If you can get past this, and the church records exist getting to the early 1700s and early may be possible.
In Czechoslovakia, in the former Austrian Empire, quite a few of the records date from the period of the 30 Years War (1618-48), whether the records are complete or not is another story. Sometimes, actually not infrequently, there are missing volumes, and you cannot get past this. Ocassionally you will see people who are described as “ vagabonds”, finding their earlier history is virtually impossible.
In Italy, civil records exist from about 1820, and in some places, from the Napoleonic period before then. Many Italian records are readily available, but not all have been preserved. Catholic records can go far back, but not many are online (due to theological differences, the Vatican has directed bishops not to allow the LDS church to microfilm records); some diocesan archives, I have been told, are making records available through their archives, but this in its early stages. Making the jump from the civil records to the church records (for those online) is theoretically possible, but in the big cities the specific church of the baptism is not identified in the birth records (perhaps unique to Italy, baptisms are noted in the civil birth records), so is difficult.
Hopefully, this gives you a sense of what can be done. It helps to have a mentor. There are a lot of resources out there.
Best of luck.
