"Is it difficult to grow long hair?"
Difficult? No. Not if you JUST want long hair...but if you want fast growing and healthy hair...that's when things get difficult (and notably more expensive

)
Here is
"Danniella's Super Awesome List of Trans Hair Care Stuff That I Totally Didn't Just Steal off of Like Lots of Other People's Hard Work, Research and Effort!"...
(the title needs work)
This should compile the best advice I have gained, and what seems to be working for me so far, organised from the least expensive/time consuming to the most...
Be Careful of Heat! : As a guy, I used to wash my hair in scorching heat and then blow dry it with a hair-dryer on the highest setting, then after a quick brush/comb I was finished and ready to start my day!...OMG I was so bad looking back on it!
Think on it this way...your hair follicles are just like any other pores on your skin, heat makes them expand and open up. So if you bath in really hot showers etc, and/or use a hair-dryer on a high heat setting, then just leave your hair, or even worse brush it, you will find yourself pulling out lots of hairs that are perfectly healthy, strong, and most importantly in this scenario, long! This is simply because your hair's grip on your pore/scalp is GREATLY reduced when the scalp is under such intense heat.
To remedy this, if you have hot showers, when you finish up, turn the shower to cold and blast your scalp for a bit (not just your hair, I KNOW it's cold and feels like a shock, but it needs to be the scalp, sure as hell helps wake you up in the morning too).
This will seal the pores and prevent your hair from coming out when it shouldn't. By the same token, you will now probably realise just why hair-dryers have a "cold" setting

After using the hot setting, cool down your scalp with the cold setting before doing any serious brushing or styling...BETTER YET! Cool your scalp and then do something else, put on clothes or make-up, BEFORE you even touch your hair (wrap it up in a nice girly manner with a towel if you want

) That way you are guaranteeing that all your hard work isn't going to all come out the instant you use your brush.
Scalp Massaging: Get a partner or do it yourself, even just 10-15mins a night. Stimulating blood flow to the follicles in your scalp is a very important part of growing your hair fast, if you encourage a healthy blood-flow to your scalp you will greatly increase the speed of your hair growth. (this is why you may notice that allot of salon hair care products for hair growth make your scalp feel warm or tingly when applied, they are just chemically heating your scalp to increase blood flow) not to mention it feels awesome ^^
Diet: Fish oils etc are good for strength and thickness of your hair (which is what you REALLY want if you are going long, you need to reduce the amount of breakages and split ends) If you don't have much in your diet, a supplement will service, but you should really be eating more fish anyway
Regular Trims: Yes you should still go to the salon even when you are growing your hair! Do not just let it grow for 2 years and expect a good result! As it grows, your hair splits at the ends, but continues to grow. Even just getting a cm or two off every every 4-6 weeks is normally enough. Without this, your hair will still grow, but it will be in a terrible, nigh on unusable condition when it finally does get to the length you desire. Keeping it healthy, thick and without split ends is paramount, and regular trims are the only way to ensure that. Express to your stylist that you are growing it out and, so long as you have a good hair dresser and not a hack, will be able to provide you with cuts etc that will look good, and not hinder the growing process.
Good hair products: Check with your salon for recommendations for your hair specifically, everybody's hair (and more importantly when discussing Growth) scalp is different. You should get professional advice to make sure you are using the right products for you...But be prepared...most supermarket brands are just utter garbage. It's more expensive, but once you start using lovely high quality salon products, you will see and feel the results, and never want to go back!
Fiasteride: Yup, it really helps with receding hair lines, but be aware that on average it can only bring your hairline back to what it was around 7 years ago, you won't get much more than that. So look back to photos of yourself from 2007, that's around what you can realistically expect after around 6-8 months on finasteride. (as a bonus feminising effect, it gives you longer and thicker eyelashes too!). You only need a very small dose though, don't go overboard or you will just be throwing your money down the drain.
Biotin: Increases the rate of hair and nail growth that's for sure,
BUT BE CAREFUL! I very rarely see people post about the negative effects of Biotin. Yes it will grow your hair fast, but it can and will
RUIN your skin if you are not careful! :S Unless you drink like an absolute fish 24/7 you will get acne breakouts and your skin will become much greasier. Like I say, I tried it for a while and yes it works, but beware the side effects, and ask yourself if they are worth the extra inch or so per month.
In addition the 5000mg doses people often recommend are far more than you need, I would suggest, if you are wanting to include biotin in your plan, that you look for a multivitamin tablet that includes a smaller dose instead of taking big doses. This is allot more common than you think.
HRT: HRT will ofc help with your hair loss and growth, Anti-Adrogens break off the DHT in your scalp and prevent it from re-forming (the same thing finasteride does), so you will see some improvement once you begin. But as will all things HRT related, the are not magic pills, and taking them alone will not result in beautiful flowing locks of hair

So yeah, there are a bunch of things you can do, what you choose, and how much you do it is up to you, and ofc YMMV
After doing all of the above (aside from taking biotin) The following pictures show my own growth.
Bit blurry, and small...but getting good picks of me pre transition is hard...
Me 4 months laterMy hair is actually longer than it looks in the second picture, as I applied volume and curled/styled the lower hanging parts. When straightened, it's almost at my chin on the sides, past my eyes at the front, and just touching the top of my spine at the back. It went from very short, fairly thin and brittle with around 3cm receding hairline, to nice thick and healthy hair, with my hairline having moved forward around 1.5cm. All in, it has grown around 11in -12in inches in 4 months (around 2-3 inches per month, which is far above the average 0.5in - 1in per month) and that is still with haircuts once every 4-6 weeks.
Hope this helps ^^