I agree with all of that apart from this comment
I used to go for average odds of 1.60...and yes, as you say, hitting them 65% of the time allowed me to break even. However, for a little while now I have been hitting much higher odds, 2.00, 3.00, 4.00...this is the way to do it. I only have a 47% success but I have staked well and that has allowed me to get to +29% ROI.
Anything is possible
It's true, technically speaking you can hit 90% and still come out with a loss. If you are staking say 1k 9 times at 1/2, then you come out with a profit of 4.5k, if you then go and blow a 5k bet at 1/10.
You come out 500 down, but yet 9 times out of 10 you were hitting.
The 65% is just a generally understood percentage, if you are playing consistent stakes, at consistent prices.
We know that things aren't necessarily like that, but what newcomers to the world of gambling should be aware of, is that if you can't even predict 65% to begin with, you should not try to take it up as anything more than an occasionally, inexpensive hobby. And I think that's a mistake people make who think this is an easy business. Every gambler has their bad periods, and I've had some pretty dark days myself at times, and basically my advice to people is stay away unless you have utmost confidence in what you are doing, have the stats to back up your belief in your ability, and are prepared for some very very bad moments, because they WILL happen to you no matter how good you are.
Another bit of advice of course to Yashirobai, is don't "chase". If you're unfamiliar with this term, it means when you lose, and feel the need (which you will) to make it back ASAP, and end up rushing into a pick that really you were not going to play at the start of the day.
All gamblers have chased at one time or another - much easier to give advice than take your own at times - and anyone will tell you, it hurts very bad. So make sure you get a handle on that discipline, because it's one of the main ones that if you don't get a hold of, can lead you to a slippery slope.
For the record Yashirobai, I know I may be coming across as the Grim Reaper with the stuff I'm telling you, but you asked for advice, so you should know the potential pitfalls as well as the possible benefits.
I liken gambling to being a shutdown corner in the NFL. No matter how fucking good you are, there will be times when you get burned. And if you don't have it in you to get up again and do it all over again, you should think very carefully before you start playing numbers you won't be able to handle.
Hope some of the things I've said will be helpful for you, and I'm sure others will chip in with their experiences too.