Building metabolism?

This is a tricky subject because there is so much disinformation out there on what metabolism rates are and how they can be tweaked. A lot of what determines metabolism is genetically based as you mention. Your BMR, basal metabolic rate, can only be increased further if you raise your body weight. You and a friend could weigh exactly the same, but because of genetics your true BMR's are slightly different. BMR calculators only give you an estimate. Over time the slight difference between you and that friend can make a huge difference on weight loss. However there is something you can do to fight this:

One thing that is well within your ability to control is to raise your total calorie burn by increasing your cardio activity. I would not just look at workouts but also lifestyle habits- they all add up. For calorie burn, cardio gives you the best bang for your buck. While strength training is not as effective in burning calories it is still very vital to keep a solid routine as well (don't give it up!). More muscle means more BMR to maintain that muscle- just keep in mind that this is not the end all as some will say. It is a factor but not the most effective factor. Many people, who are not as metabolically blessed, will get frustrated because they have followed the hype and are probably mainly doing a strength (weight bearing) routine with little or less emphasis on cardio. They see countless examples of folks that do this and have fantastic results. Its just that these folks don't have the same BMR challenges and thus their strategy still is effective for them. This can be fixed if you put a higher emphasis on your cardio training.

So, for example, let's say that you are currently doing strength training 4 times a week and cardio 3 times a week. A good strategy would be to switch and do cardio 4x and strength 3x. If this works for you then put special emphasis on always increasing the intensity and time, when you can, of your cardio work as much as feasible.

Diet habits can also have an influence. The ultimate effect is obviously running an effective calorie deficit, not too high, not too low. But also our bodies spend a good amount of energy digesting food as well and more of that energy is expended if we spread out our meals but this too is often way over exaggerated. The difference in 1 meal a day vs 5-6 meals a day is there but by itself will make little impact.

Stay at it and maintain patience. Think of your aerobic/cardio exercise as what will give you results more quickly but your weight training and the resulting increased musculature (which does not mean bulk but means sexy shape on ladies!) will be what gives you the more long term results and maintenance.

ETA; But also remember that 70-80% of this is diet. Not just what you eat and how much but when you eat. The key to diet is having good information and winning the mental game. You want to keep your blood sugar, mood and energy levels as consistent as possible to prevent metabolism slow downs. Ironically, I would also look into intermittent fasting (IF for short). I say ironically because when done well it not only helps you with your calorie deficit but also helps you to increase the mastery over your metabolism ( and here I will add to that your hunger levels and energy levels). Metabolism is about enzymes and hormones but it can be boiled down to how efficiently you convert food to energy and then how efficiently you burn that energy. Our bodies are brilliant at adjusting and becoming efficient to maintain and increase body weight with what's given to them- aka survival mode. Our bodies main goal is to prevent starvation. So things like a strategic diet, cardio, muscle build and IF can throw that off a bit and allow you to 'insert' break throughs and actually lose that unwanted weight. Its always easier when someone is at their heaviest and are just starting out because our BMR is higher when we weigh more so anything we do has dramatic results. But as we lose weight this effectiveness rate lessens and so we have to work smarter. So, our best bet is to find the quickest and most efficient means to reach our goals without burning out. So things like walking and cutting sugar may have worked many months and pounds ago but now its running, compound movement heavy weight training and a whole diet makeover as an example.

Increase your NEAT. (Move more).

Meal frequency will not effect expenditure at all given the same total intake, as it's based on the expenditure requirement to process food. Eating more frequently with the same total intake just means you're expending less energy per meal since you're eating less.

See here:
www.myfitnesspal.com/topics/show/529002-a-compliation-on-meal-frequency

You really need to just create a calorie deficit and increase your activity outside of the gym, in addition to your in-gym training.