Very nice shawl and I think it's very do-able.
The instructions for the first 4 rows help you place the lace pattern sts in the center of the piece and show you how to make the increases.
"Continue in estalished pattern" means to keep knitting the edge sts as you have in rows 1-4 and proceed with the next rows of the lace pattern over the center sts. You'll be working the first and last 4sts in garter stitch. The yo will be worked in stockinette, purl on the WS and knit on the RS.
When you finish row 12 of the lace pattern, start again with row 1 of the lace pattern for the center panel. The instructions for the increase row, row 5, tell you where to place the yo (next to the garter stitch edges). You'll repeat the yo increase on rows 9, i, 5, 9, 1, 5, 9 and so on as you repeat the lace pattern.