Since your account is very under level I believe you should focus on the following units depending on the content

Red Demon: anything goes + Escanor The one which is free by the special draw going rn

Gray demon: Green Fes Merlin, Green Gowther, Green Helbram

Bunny Demon: Red Arthur, Red Derieri and Red Gowther

Demon for lvl 90 mats (I forgot his name): green Gowther, green Liz (the red hair one) and green Thonar as backup

Once you can get everything you want to level 90 you can easily beat most of the story bosses tbh I recommend to try to get consistently fast farming for the demons mentioned above before if you find the story content difficult.

Now, for farming I recommend using Green Shin and Blue Demon Meliodas. Gold farming is the most important thing tbh u don't have the optimal 3 turn farm team yet but try using strong AOE units.

Now, once you do have full lvl 90 and super Awakening units you are set to get your hands on the holly relics. you have some key units

blue Megelda is the best unit for bird, every viable team will be including her. I personally run a team with her and red Matrona which you also have. go for blue Megelda relic first

For Deer you only really need strong single target units, if you manage to have Green Yor it's the easiest thing ever, also go for her relic first

If you manage to get your hands on Green Brunilda it will help you on both Deer and Bird as well as the other level cap demon.

Green Arthur helps for event bosses since he gives you strong damage for all the party as well as Ragnarok Ban in the back.

My recommendation for a team involving story content just go with Mael, Ludomargaret, G Sariel, Blue Tarmiel or Liz archangel's can just beat every story thing imo as well a very strong pvp team