I can report some information on Mahamevnawa. I find it unfortunate there isn't much about them in english on the internet.
First, from what I've heard there, Mahamevnawa is the biggest order in Sri Lanka. There are some 40 branches in the island and a bunch around the world . While it is a forrest tradition, some monasteries can be quite busy, but others are extremely secluded, ideal for those ready for deepening their practice.
The chief monk there is ven. Kiribathgoda Ñanananda , who translated the entire sutta pitaka to modern sinhala in the last couple of decades. He is highly and widely respected for his work on restoring Buddhism in Sri Lanka, where I was told it was common for monks to play with horoscopes to see if someone would go to heaven, hell, or have merits to attain arahatship... things like that.
So, in Mahamevnawa, you will hear that the suttas are the greatest authority. Commentaries are seen as commentaries, and the Abhidhamma contents, as far as I saw, were seldom a subject of conversation.
One important thing also is that they are quite rigorous about vinaya. I find it particularly important that monks are not allowed electronic gadgets: notebooks, pads, smart phones. Only a handful of monks were authorized to use the computers in the Polgahawela monastery for very specific tasks.
The ideal first step for ordination in Mahamevnawa is to be familiar with one of their temples, if you are lucky to have one near by. Then, they can get to know you (you get to know them) and it's easier for them to help with permanent visa to Sri Lanka. Otherwise, you will have to get a tourist visa to stay in the monastery in Sri Lanka, and from there, they can help with visa extensions and permanent visa application. However, be reminded that, as of now, you must leave Sri Lanka and come back to perform this visa operation from tourist to resident. Not only that, but also it seems Sri Lanka's immigration policy requires the person to go back to the country of origin before returning to Sri Lanka with a permanent visa.
Of course, contact them through email before going and plan with them your visit. They are very kind and quick to respond, and very interested in learning about you and answering any questions you might have through email.
Once in the monastery, probably the headquarters in Polgahawela, you will have to live there for a few months as a candidate along with many dozen of other candidates. In the Polgahawela monastery, there are usually 80 to 100 monks. Day to day activities include chores, pujja cerimonies and classes (dhamma/sutta classes, dhamma talk classes and chanting classes). These are in sinhala, but they work to provide the english speaking candidates with classes as well. There are very few westerners in Mahamevnawa, but there's always people (candidate and monks) around who can speak english, so it's not overly isolated for those who can't speak the local language as it could be in other monasteries around the world.
As a candidate, they also encourage you to meditate whenever there's free time. There are always monks to help you, but for the most part, questions of individual practice are usually directed to the ven. Ñanananda who is always available and, of course, is very experienced.
Naturally, once there, you should try your best to learn Sinhala. There are some english books in the library to learn sinhala, and people there can put a lot of effort to help you too.
Once ordained as a samanera, I believe it takes around one year or so until one is eligible for higher ordination. Also, as a samanera, one has a lot of free and individual time in their hands, though there are still classes available for ordained ones, including Pali classes.
Also, monks rotate quite frequently in Mahamevnawa. Every six months, they are assigned to different monasteries in Sri Lanka. More experienced monks also travel overseas. This is a great policy, as it prevents monks from forming intimate ties with the lay people, and prevents them from getting attached to place and people. It also puts one in contact with different monks. Similarly, Mahamevnawa monasteries also frequently receive guest monks from different countries and different traditions.
Finally, Sinhalese people are very warm, kind and friendly folks, which is great news for those coming from other countries. The food is very good, though it can be very spicy. But there's always not-so-spicy options too.
In a gist, I believe the general spirit of Mahamevnawa is of a sincere attempt to stick to the Buddha's words and implement what he taught. As I was told and witnessed, it's a community that sees each other as kalyana mitta. They are genuinely interested and always remind you that everything there is to help one to attain the fruits of the path, always in light of the words of the Buddha preserved in the Pali tradition. This also means they take a much more carefully crafted road, providing the monks with a solid foundation and education, instead of sending them right away to a cave; too much experiences with watching people get deluded and disrobe in a few months. In other words, they take the perspective that this is an education for the rest of your life, and that it takes a lot of patience to develop the qualities and skills for climbing the wisdom mountain.
Hope this helps! Godspeed!
 - https://en.wikipedia.org/wiki/List_of_M ... a_branches
 - https://en.wikipedia.org/wiki/Kiribathg ... anda_Thero