Hope this helps...
Something to consider, forget caliber. Couple questions to ask your self before purchasing a firearm, (pistol or rifle)
-What is the intended use; concealed carry, self defence, home defence, range gun, competition shooting... etc etc
-are you prepared to become intimetly familiar with the firearm, use and function
-what is your price range, can you afford the time, use, and maintenece costs
Any caliber can be deadly, even the meager .22LR, it all comes to shot placement.
On the points above, if the intended use is a carry role you need to find something to fit your style of clothing and body shape but also small, light and comfortable enough to carry everyday. The gun is worthless if it is sitting at your house and you are out because it is uncomfortable to carry all day everyday. If it is strictly home defence then make it as big as you can reliably be consistenly accurate with. Plinking/range gun lower caliber =less cost, (.22lr a lot cheaper although not as fun as .45 acp)
To buy use and own a gun makes it part of you, you need to know everything about it to utilize it to its potential. How to strip, clean, reassemble, shoot, and store it all goes to how the gun performs. 95% of inaccurate shooting is the shooter (my guestimated stat but one I am comfortable stating)
Now price, the initial purchase is the biggest part to overcome, a lot of people say you get what you pay for, but I dissagree. My taurus 85 shoots just as good for a 200$ gun as a more expensive colt. A kel tec pf9 can be just as accurate and reliable as a kahr pm9, it all comes down to the person behind the gun. If you want a specific gun because it is just cool, that's ok. Think about the firearms POU (philociphy of use, Nutnfancy's term youtube check him out) what do you intend the gun to do. Just my 2 cents good luck