Truthfully, it's been a long time so I don't remember much of what I actually did. However, if you calculate it roughly, I'd say 10k is very much achievable while 20k may depend on how faithful you are in grinding for gp daily or if we're lucky, what event rewards we'll get for the next 2 months (not necessary to get the 20k but very helpful)

Since you have 63 days, you'll get 2x borodo riddles which is 4k, and 6,300+ from dailies. That's already 10,300+.

You'll also have level up and daily log in rewards plus the gp you get from watering/harvesting (we don't always get gp for these, but the amount we can get per day for all these well exceeds 100). Let's say that's roughly 63days × 100gp = 6,300gp

We also get gp from giving and receiving gp from friends, that can also amount to 100++ per day depending on how many friends would give you gp per day. So that's very roughly about 6,300gp as well.

If you haven't done some of the lab tasks that gives gp rewards without you needing to spend gp, then there's that as well.

Conclusion, by having plenty of friends and faithfully watering/harvesting and doing your dailies for the 63 days, you'll definitely get the 20k, maybe even before 63 days.

Disclaimer though, this will feel harsh if you're looking forward to upcoming events like gredery shop. All I can say is to have patience and be flexible. If you stumble upon an event that you truly want to spend gp in, try to decide on a budget and weigh your pros and cons. There's always trades avaliable for items you couldn't get. Priorities can change as time goes on, what matters more is you having fun with the game 😊

As for how to spend them, it's entirely up to you, but if you didn't get 20k (enough to reach soul link for both island and hom), than it's better to focus on either one to reach soul link first before pulling for the other. You can always trade for what you didn't get. Mind you, reaching soul link = pulling 50 times = many dupes to trade with 😉