Higher arena scores?

The exact amounts of score increases and their causes are incredibly cryptic (at least to my knowledge).

As far as I know, each merge gets you an arena point, each 10 extra points in BST get you an arena point. Inheriting more SP expensive skills to your heroes gives you some kind of an increase (never found the numbers for it), which means that skills like growing wind and those blazing things will help in some way and having the third levels of skills will always be better than having just lvl 2. Having a fully skill equipped hero makes his arena weight higher. Replacing a hero's original skill gives him higher weight (eg. Replacing spur speed with drive speed).

That's all I know. Just go for a team of Ike, Amelia, Effie and a bonus hero and you should do fine as far as points go.

Amelia with a full set of skills will be very heavy as the highest BST hero in game so try to run her with your arena team always. You want either a 5-star or a 4-star merge of the bonus heroes if possible or you'll never make the next tier each week as well. Characters with Aether and Galeforce (or inherited it) have more arena weight as well.

If you can build it, full armor emblem is the highest base score team you can get followed by dragon emblem because if the higher base stats they all have as well.

I suggest investing in the 3 starter characters, even just get them to 4 star level 40 with decent skills. That way you always have a bonus hero.

As for your core team, I'd suggest Ike, Tana, Hector. They can deal with just about any threat. Tana and Ike having reposition will help very much, you'll find yourself out of some otherwise impossible positions using it.

That team can definitely make it into tier 19 with a drathless run. If their fully built, probably tier 20. You'll never maintain tier 20 without heavily merged units though. You should be able to bounce back and forth from 19-20.

Higher BST equals more Arena weighting and a higher score. Skills that cost more SP equals more Arena weighting and a higher score.

The exact way the score is calculated is still unknown so we can't actually know for certain what rating/points we'll get.

From personal experience however, the SP cost of skills actually provide more rating than BST. My Reinhardt running things like Growing Wind (300 as compared to 200), Quick Reposte 3 (240 as compared to 200), and his Legendary/Uninheritable Dire Thunder (400 as compared to 300) actually gave my Rein more rating than my Brave Lance Effie which is pretty insane since we're comparing one of the lowest BST units to one of the highest.

Another example is my Brave Ike with his base kit with only 5 more BST than my fully built Brave Axe Cherche single handedly gave me about 30-40 more points in a full Arena run.

All valid and accurate points. I would add that legendary weapons (ones that cannot be inherited) also offer more weight.

Based on your roster, your potential should be tier 19 and above.

Here's how arena scoring works. Your score depends on how strong your opponents are, and selections of your opponents depend on how strong you are. So, if you fit FEH's criterion of "strong," you'll be matched with "strong" opponents that give you high scores.

There's a variety of factors that determine strongness: 1) BST (hence armor units are great for arena weighting in general; 2) legendary weapons (hence Brave Lyn is actually very decent in arena weighting); 3) skills in terms of SP costs (thus using Aether would be a huge advantage if you can still maintain deathless runs); and 4) merge levels (not sure if it's due to the increase in BST or merge itself, but either way it impacts your arena weight).

Based on the above criterion and your roster and considering the importance of achieving deathless runs, I'd suggest you form a team with core units like Hector/Amelia, Effie, Tana, Brave Lyn, Brave Lucina, and Ike. Of course, you only need three of them since the 4th spot is reserved for the bonus unit.

Personally, I'd go for two teams. 1) Hector, Nowi, Ike, and bonus unit. This team has color coverage and built-in DC, so it's a budget team that's also effective. 2) Amelia, Effie, Brave Lyn, and bonus unit. Due to Amelia's Armor March, Effie can move two spaces and thus does not need DC to be effective. Brave Lyn can cover mages with her legendary weapon. This team will weigh quite heavily as well.

Hope it helps. Have fun.