I got into ancients for a few years, and really did love them. I am sorry I did not keep up with it. It is so difficult to complete any ancient sets, but I really love the tetradrachms from the 2nd-4th century B.C. I still have my Ptolemy II tet.
I fear your preferences are going to make it difficult to profit. It's not necessary to specialize to make money but you do need focus. You must learn to recognize rarity when you see it. Sometimes a $20 coin is far rarer than a $10,000 coin and if you judge rarity by price alone you will end up with the mundane or at best a fully priced collection of scarcities. Ancients and foreign coins are good suggestions. A type set is also a good suggestion if you take your time and learn. Sell some coins once in a while so you know the real spread between buy and sell. You might consider trying some super cheap collection like tax tokens (really coins) as you're learning the markets and the coins. This might satisfy your need to buy without exposing you to unnecessary risk. Good luck.
Since it hasn't been suggested outright yet I suggest modern world coins. You can define modern, but I go with 1900s on up. There's so much variety and history: occupation coinage, zinc coins, type sets, condition rarities, design similarities, gold, etc. You name it. I also collect US coins, probably a tad more than most other countries, but it's still just one other country to me to collect
I don't collect ancients but I get the impression that those who do around here really know their stuff.