I'm on my last eyelids, so sorry if something not accurate.
First question. Oh, this backpack looks nice, but that one too. Which to choose?
Actually both are used.
You see, Arnval (and Strarf) are the only shinkis that have two Ultimate RA. Yes two.
There is a catch tough. You can only choose one in battle since for arnval, one RA use different backpack and leg part than the other.
Don't worry, you can just choose the RA and the AI ask you if you want to equip the neccessary parts for the Ultimate RA. The problem is which Ultimate's who. Since in your case it is only Arnval, it should be easy. However when you have 15 or more...you need to at least know it.
Second ultimate RA only gotten from love event battle.
Not true. You just need to get her love to 20 and see her event. At home, you can press start and choose the second option to see how much love event you have seen for a particular shinki. Arnval got it at around event number 12 from a total of 17 love event.
Third Club Valhalla where you can get money and good parts...or being robbed blindly.
Club Valhalla will open as the story goes during the qualifying of F1 tournament. You can find it at the upper right side of the map.
The battle system is just iike at the game centre with a twist. The good thing is, the opponent there have good equip, so if you manage to defeat them, you get a little money and most importantly one till four of their equip. The bad thing is, most of them will have equip at least lvl 4 which means they are strong. Some of them even have ultimate RA and won't be shy to use it if you give them chance and if you lose, the AI will randomly TAKE one of your parts.
Fourth the junk shop. Hey that weapon looks nice and it is cheap...because there is a catch.
Most of these weapons are with +IR and +GR.
Let me say the good part 1st.
For their price and their cost to equip, they are very powerful. And while most weapon gives only skill related to the weapon (ex. 1h sword give +1 to gatling), they give some good skills like Lock on range+1
Now for the bad.
They also have some bad skills attach to them. Maybe minus to speed or dex or something. Range weapon of these families can't be charged (ex like rifle), but the melee weapon that really stinks. If you want to combo using it, you must press the combo at a certain time, usually during a shinki shout, groan, sound. But during the heat of the battle, I can't even think about perfect timing.
And something like selling? No, it is Junking your shinki, where despite all her love for you, you throw her away like a trash. Will I do that? No, HELL NO. No matter what the reason I will never throw away my shinkis. Will you?
5th question. Is Strarf hand armor like Altines? And who is those two anyway?
You mean static and never moved? Yea.
Those two...if I'm not mistaken, those are Estoril and JillRivers.
Estoril is the pink haired with pink racing attire.
JillRivers the blue ponytailed with black suit. I want to named her Mio but ends up with a dash. Don't ask.
Hmmm, Justice don't have event. Looks like Arnval/Altlene and DLC? If you are talking about with long hair, and black curvy suit with gold ornament, that is Sharatang.
If that one with ponytail and white suit and black ornament, most likely is Proxima.
Edit: Aw, OshareKeiji already answer it. Guess you can ignore this I guess.
"Motto Shiawase Ni Naru"