I have a feeling there is too much information being thrown here so lets boil it down a little bit:
1. focus on arrows with speed primaries, 3 star or + untill you get a 5*
2. focus on speed SECONDARIES on other mods.
3. THE MOD TYPE DOES NOT MATTER AT THE MOMENT (I have a feeling this is your biggest issue and it was mine as well. You simply do not have access to speed type mods yet. Few people do. Especially 5* simmable access. While they are better than HP mods, HP mods are much more accessible. and you need 4x speed mods to get a 10% speed boost. That will translate to 15-20 speed, and for that not only do you need 4 5 star speed mods, you need them to be a speed arrow and have speed secondaries, since those are meta mods. FOCUS ON 5* MODS YOU CAN ACCESS, ASAP)
4. In adition to the 30 mods you will use for your arena, you will need 5* mods for your ships and admirals (Mace, Tarkin, the squid or Thrawn) And that is 42-60 mods, all leveled up to max, eventually (the numbers vary depending on how many ships you can use). The good part is THE STATS AND TYPES ON THOSE MODS DO NOT CONTRIBUTE. Only the level and stars do. So your ezra arrow, while useless on ezra in arena, will contribute the same to a biggs pilot as a super nice 30 speed arrow.
5. You can level a mod to lvl 12 to see all the stats it will have. This is only 30% of the price it takes to level it to max (lvl 1-14 is just slightly more than 14-15) So take that into account as well.