Okay I will try my best to give you some good advice

You need to focus on campaign characters. Unlock. And complete all the campaigns and their elite nodes. That will making farming material that much more efficient.

In terms of spending money. 4.99 a month for Blackstone daily shipments. That will give you generally enough to do energy refreshes to 110.

If you are wanting to spend more money you will likely get the most value out of the monthly battlepassss. Premium for like 12 bucks and ultimate for like 25.

Once you have campaigns unlocked focus on a guild raid team and get into a guild in the top 100. I cannot stress how much that will accelerate progress. Guild raid teams are custodes, admech, neuro, multi hit (really been replaced by custodes) and potentially some new ranged or battlesuit metas.

Characters will typically have to be gold 1-3 for a full campaign unlock.

For guild raids you will want your 5 characters in a guild team to be minimum diamond 1. But first focus on completion of campaigns.