I think Western (and many credit unions) are a bit simpler than the stats you listed. Being small organizations, they don't have a bunch of employees coming up with their own risk models (versus what you might have at a big bank like Chase), so that's why they're paying Fair Isaac for the FICO score. As a result, I think the APR is often entirely set based on FICO (740 on EXP at Western was the top rate when I called in the past). You can call many credit unions, and while their front line bank or customer service reps might not know (and you'll get the cop out, "We consider a lot of factors!") answer, their more experienced loan officers or analysts will tell you what FICO you need for the best rates.
Size of the credit line issued to you is much more subjective and dependent on the credit analyst you get. I have high income, so that's never a problem. Many credit unions care about their own experience with you, and won't give you the highest credit line you qualify for right away. Since I already had a small personal loan (10K) and an auto loan (5K) for a short time with no problem paying, I got a 30K credit card when I first applied at Western. I waited until I had a fico of just over 740 to apply since that's what they told me that I needed for the best rate. I suspect it would have been more like 10k or 15K if it was the first account I had with them. After that, adding a LOC and growing the CC was based on how long I had the previous account.. e.g. They would like to see you manage what you have for around 1 year before raising it. I would guess that 10K or 15K annual increases per account is typical if your income supports it, even if your FICO was more like 700 (though the higher the FICO, the higher the increase).
More recently, I applied to a couple of credit unions while taking advantage of a lot of 0% APR offers (hurting my utilization %, size of debt, and FICO).
At BECU, I think my FICO was just over 700, and I was initially offered 15K on the credit card and 15K on the LOC. The interest rates were ~2% higher than their best rate since my FICO was not above 740. I'll apply for a credit limit increase next time my score is over 740, and I bet they will give their max credit lines (25K each) for the CC and LOC + best apr.
A few months later, with an even lower FICO I tried at Apple FCU (TU 675), State Department FCU (EX 705), and DCU (EQ 671) and got nothing. Their listed reasons were "Amount owed on Revolving Accounts", "Number of recent accounts", "Proportion of balances to credit limits too high on revolving accounts" respectively.
So back to your situation based on my experience and what I hear from others..
For a typical mass market bank or credit union, I often hear between 25% and 50% of a person's income as the maximum amount of credit they will extend to a person. However, I also think it's hard to get more than 10K or 15K per credit line at a bank that you have no previous history with, even if your FICO and income support it. As a result, I think you can grow your credit line at a bank to get 25K+, but if you want it immediately from new banks, you'll probably need to apply to more than one bank or multiple products (cc + loc). However, I think its nice to spread my eggs around a bit since it will give plenty of opportunities to grow the lines (without adding new accounts) and give access to the special promotions various banks/CU offer from time to time.
