Yes you can apply after the first year for the HPSP. That's why the 3 year would be a good option for you (4 year HPSP needs to be obtained before starting school, I believe, because I don't think they would retroactively pay your first year's tuition). I'm not sure about WICHE funded scholarships. I know the NHSC is vastly more competitive than the HPSP and it is very rare that somebody who is not from an undeserved area gets the scholarship. There are always exceptions though.
The HPSP competitiveness depends on a lot of things. First off, there is a difference between the branches. The general consensus is Air Force>Navy>Army in terms of competitiveness. There is also a huge wildcard factor in how good your recruiter is at vouching for you, handling your paperwork, ensuring everything is done in a timely manner, etc. Anecdotally there is a wide variety of outcomes. There have been people with 3.8/23 AA that have been rejected from the Army HPSP as well as someone who managed to get a 4 year HPSP contingent upon a dental school acceptance and somehow managed to not even get into Touro. My opinion is that ****ty recruiter and applying too late or having terrible interview skills contributed to these two outcomes respectively, but who knows what really happens. Also, history of physical illness/injury in certain cases could get you disqualified from being eligible for the scholarship.
To vastly oversimplify and make assumptions, if you have a 3.7 and a 21 or 22 GPA, and a recruiter who is really in your corner, you shouldn't have a problem getting the HPSP if you apply early enough to all three branches. This is for 4 year HPSP, I don't know how different the competitiveness is for 3 year HPSP.
Word of warning, if you do HPSP solely for the money you will likely be miserable.
As for how long it will take you to pay off $400,000 in loans:
Below is a copy and pasted take on UAB vs Louisville tuition for another SDNer that I did awhile back. Your in-state vs whatever private school to which you have an acceptance will vary from what's described below, but it's a good comparison benchmark.
So let's look at cost only first. With projected tuition increases, fees and other chicken**** charges, living expenses, and interest accrued in school I have you graduating from UAB with $207,200 of debt. It's important to note that I have projected all of your loans to be unsubsidized Stafford, meaning you have the lower interest rate of 5.84%. I didn't calculate your origination fee, but it's going to make only a small increase in your balance compared to the 4% origination fee that the Grad Plus loans would from another school. We'll get into that later. So for UAB, if you wanted to repay your loans in the following amounts of time, this is what your monthly payments would look like.
5 years- $3,990.36 w/$32,221.57 of interest paid over the life of your loan
6 years- $3,418.27 w/$38,915.86 interest
7 years- $3,011.02 w/$45,726.19 interest
8 years-$2,706.79 w/$52,651.88 interest
9 years- $2,471.23 w/$59,692.71 interest
10 years- $2,283.73 w/$66,847.98 interest
Now let's take Louisville, just as an example that you had used earlier in the thread (also a decent example because it as a more OOS friendly public than some others). With rounding, unsubsidized Stafford covers around $47,000 per year. So that means that you'll be on the hook for pretty much that amount once more for the GradPlus, which has the 4% origination fee and the 6.8% interest. So, without taking into account inevitable tuition increases and going off what you have based on your table, with interest accrued during school and your origination fees you're at $446,000 of debt coming out of Louisville.
SIDE NOTE: anyone who wants explanation of these calculations just ask and I'll post them. I know $446,000 for Louisville seems too high but it's not.
So here's your Louisville repayment plan
5 years- $8,589.29/mo w/$69,357.21 interest
6 years-$7,357.87/mo w/$83,766.60 intersect
7 years-$6,481.26/mo w/$98,425.83 interest
8 years-$5,826.39/mo w/$113,333.79 interest
9 years- $5,319.34/mo w/$128,489.25 interest
10 years- $4,915.76/mo w/$143,890.41 interest
Let's say you get lucky and as an associate in a state with no state income tax you're making $150,000 a year. Let's also assume you're married with one child (both of which decrease your tax burden), and your wife makes $50,000 while being debt free (another assumption that would help you out. Of your household's $200,000 of income, you keep $164,000 of it. In order to pay off Louisville in 5 years, you would have to live off of $61,000 a year. If your wife didn't work or you were single, you'd live off of $11,000 a year. Louisville's 10 year would have you living off of $105,020 a year, or $55,020 a year if you are a one income household. However, you would be paying $74,000 extra in interest over the life of the 10 year as opposed to the 5 year.
Now let's use the same situation with UAB. You would live off of $116,120 a year or $66,120 if single income for the 5 year plan. On the 10 year you would live off $136,596 or $86,596 depending on wife status, with only $34,000 extra in interest.
So as you've said, your desire is eventually to own your own practice. These numbers pretty much put to rest the "one year not in school means one year of lost income" argument of going to a private school this cycle vs UAB next cycle. By going to a private school over UAB, you're losing much more than a year's worth of income. Hell, if you're doing the 10 year plan (which I don't recommend,but it might be your best bet down the road given your situation), it's possible that you'll be losing a year's worth of post-tax income IN INTEREST ALONE when comparing the two options.It is financial suicide to attend a private school if it's not your only option, given your scenario of wanting to open up your own GP office. You would be better off just going military and borrowing the loans to borrow the practice once you're out.