Welcome to Ultima! I'll answer your questions in order with a few of my personal tips and knowledge!
1. Techniques drop somewhat frequently in Episode 1 Ultimate but at a rate which I could not say; as Soly said, they are tool items and tool items drop less frequently than other items do. However, in Episode 1 Ultimate you should have no issues finding techniques at least level 20 and above as most techniques that drop in Ultimate tend to be lvl 20 and above depending on the area.
2. Make full use of your traps when soloing or with your sister!! Traps are absolutely the most useful tool for aspiring HUcasts looking to be efficient in both solo play and group play. Make full use of freeze traps, confuse traps, and damage traps. A little bit of knowledge you may not already know yet, Episode 1 and 4 enemies have a very strange weakness to fire; damage traps do fire damage when they hit enemies so they naturally do a good chunk of damage to a lot of dudes. I'd definitely incorporate some form trap combo system where you lie down a freeze trap and then a damage trap right after. Episode 2 enemies are not nearly as weak to damage traps as episode 1 and 4 enemies, so try and incorporate some cool combos. As for weapons, I'd definitely try to pick up some twin swords or double sabers/daggers, those end up being the bulk of your single target damage and I'd try and get something like Zanba, Chain Sawd, Red Sword, and Red Handgun much quicker. Your ID is Redria, so you can get Red Handgun from Pal Rappies quite easily, your sisters ID is Bluefull, which can drop Imperial Pick from Tollaw's in Forest 1 on Ultimate, which is a great starter Partisan weapon for you. Redria also drops God/Battle from Hildelts in Forest 2 and if you guys have enough time on your hands, your sisters Bluefull ID drops a Heaven's Punisher (Ranger only) weapon from Hildetorr's (the rare Hildelt) at a somewhat difficult rate but you can get it to sell for other stuff.
3. Max out your stats wisely. Focus your materials on stats that matter most to your class. Your sister, if she's thinking of entering a purely support/mage role should focus her materials on Mind primarily, you should definitely focus your materials on a mix of Luck and Power, while also making sure you have a mag that has the baseline ATA stat requirement. As a HUcast, your ATA stat is key to you dealing damage; in fact, I would worry a lot less about the ATP value you have and direct all your attention to making sure your ATA stat is maxed as you wont be able to hit anything in Ultimate with low ATA. Don't pool all your mag points into DEX but don't neglect it either. There are plenty of build guides on Ultima around HUcast. What mats to use, how many, how to build your mag, etc. All characters on Ultima got a stat boost of +100 to their max ATP stat and +10 to their max ATA stat. So instead of maxing HUcast ATP at 16xx you max it out at 17xx which is a big boost.
If you need any more help, you can find me on or message me on forums for help. I have a ton of spare Heavenly/power units and arms available for you to use and I have spare techniques I collect for your sister to use. I'll be glad to help you get gear and give you some essentials to make your life easier. Hope you enjoy your stay.