You should have 150 to 200 yards of backing (30 lbs.) on 4 to 4.5 inches reel.

Splicing is not that hard, practices on some scrap piece of line first then go for it.

That weight rod will take 630 to 720 grains approx. without seeing the rod I can’t be sure. Here is a formula for a 640 grain tip line belly section:

Reel end
22 ¾” of 10 wt.
35” of 11 wt.
160” of 14 wt.
85 ¾” of 12 wt.
86” of 11 wt.
Tip end

Then just add your sink-tips (135 to 145 grain)