LIFE
You might reconsider if it's worth taking 4 hours travel to go play poker. Unless you do it once a month or so. I'd tell you to find a better way to make money perhaps. Poker is a tyring, stressfull game. If you play too long and have to travel 2 hours to go and 2 hours to come back you might consider that one day you might get an accident because you're too tired and you decided to still keep driving.
Also your wife seems to not really approve your choices to 100%, you would make her really happy if you stopped playing i guess.
POKER
You should consider enter with full stack if you think you have the edge over other players. If you don't have an edge why play?
The fact that you have to keep track all the time of how much money you have or how much you are down just keeps distracting you from the current play. Focus on the game and you can check of your up and down after you quit for the day or if you loose your stack.
I don't like the strategy to pull back when you get -200$. It basically means you lost a big pot. Which will happen time to time.
What you should consider is not how much you are down, but more likely how good is your game on that day after you loose a big pot like that. Maybe you played well but the player got lucky and you might be able to get the money back later on. If you quit now that person might be in different mental state or might not be back next time you come. If it's a fish you might want to keep sticking around and try get his money.
If you think your mental state is affected by the big loss you should consider go home which i think would be the best decision.
My strategy is always to have 2 full stacks(2x300=600$ in this case) and that's what i play for in the day. If i go up i try to keep growing(lets say i reached 800$). Sometimes if i feel like there are too many good players with good stack(around >=600) i would stand up take my chips and come back a few minutes later with lower stack(300$ buy in). Normally i only stop if i start to make mistakes, start to get too tired or the casino closes.European casinos not open 24/h :(
With this strategy i don't really loose my momentum.
Another problem you have is your wife's rule 20/80. At some point you will loose all your bankroll because of that rule.
Let's say you started with 300$ you manage to double up 600$ and decide to go home.
You have 300$ so 20% of 300$ = 60$ which you will have to deduce all expenses which makes you basically go to almost nothing. Sometimes you will break even days like that happen. On those days you will than loose some money. And unless you can win 1000$ per session i don't think you will be able to survive for a long time.Try negotiate a 50/50 rule at least it will get you keep play if you're a good player.
All this will affect your mental state and you will start to play really tight. You might also fold in places where you think it's too risky because it affects your bankroll too much or you still want to keep playing for the day.
The best and most effective way to play is to have 1 or more stack and just play with it without constrains.