Your last question is not an easy one. Sometimes the direct odds you are getting might make it fine to call, but some hands/positions/opponents can change that decision. You can use the calculator I linked to see how much equity you need to make a call break-even or profitable. Then you can use Equilab or a website to estimate what your equity is, but it isn’t that simple.
In the example I gave, I call with 27o, but in reality you may not want to do that even with the best price. The reason being, 27o can get you into a lot of trouble and be tough to win with, even if you hit the board. Even if you have two pair or trips, you can be way behind, and you will never have two-card flushes or straights. Hands like suited cards and connected cards hit boards better and have better playability than other hands. For example, I love 54s and hate A6o, even though A6o has a much greater overall equity preflop.
Against one opponent with a strong range, the worst hand is 27o with about 21% equity against a range I assigned. If you needed to call 100 to win 400, you would be getting the right price. BUT, for the pot to be that big relative to your call, there would have to be multiple opponents, so your equity share would be even smaller. So, the guess of about 6 to 1 seems about right, but playing any two cards is rarely a good decision. I used that example to put the small bet size into perspective.
To answer your first question, because everyone calls the big blind in your 25/50 game, that is a reason to bet even bigger. Punish them for playing passively, apply pressure, have fewer multi-way pots, and win bigger pots when you have a good hand. My default raise size is 3.5 big blinds +1 for every limper, but in that game I might start with 5 big blinds and go up from there.
Equating Replay to real money poker is difficult because even the best players here are often not experienced real-money players. I have played maybe a few thousand hands of $1/2 live in casinos and won a few hundred dollars. From what I saw of the play, it is most similar to about the 50000/100000 chip stakes here on Replay. Players there are a bit less passive than Replay, but some of them are quite bad and a few are good.
Learning the basic skills on The Poker Bank and Upswing Poker will enable you to beat Replay by playing ABC poker, and it should enable you to also beat live $1/2 games. With the skills to accrue hundreds of millions or billions of chips on Replay, it should be possible to make a few hundred dollars a week consistently at live $1/2 if you play 3+ hour sessions every day. This is just speculation on my part, and I highly doubt that it would be possible to earn a living in the United States doing this as a full time job.
Online is a whole other beast, and the skill level is much higher. I have only played about 15k hands of 2NL/5NL/10NL on ACR, and was able to win consistently, but it is a small sample size. The play was much more active than Replay and probably stronger than live $1/2. I have also played a few hundred hands of 25NL, but not enough to get a sense of it. The game supposedly gets much harder each level from 25NL up, even there you are not winning significant amounts of money. Even with the high winrate I had at 5NL/10NL, I was winning like $10 or $20 in a session. It does seem possible to win like $20 a week pretty easily if you played 10NL for like 20 hours a week, but again, just speculating, and that is not a great hourly rate compared to any job.