Howlong, classic ! Didn't know it existed, but just up the road from Albury!
So, you live on the Murray River, so you'll get plenty of opportunity to rack up some flat water hours!
As per CMC, Aussie made can be a good option for various reasons.
This board is light, well made, and Aussie. Very good for flat water, and will be OK in the surf, although not strictly built for the surf
www.seabreeze.com.au/Classifieds/Stand%20Up%20Paddle/~rntjp/2009-Dc-Dale-Chapman-126-12-6.aspx?search=uQNVTXNc1pVmLaT%2fQ5QGqg%3d%3dHere's a 2nd hand 10'0 Mana that DJ mentioned. These boards have loads of volume, for your weight. 210 Litres, but some other 10'0 boards might be closer to 150 litres.
www.seabreeze.com.au/Classifieds/Stand%20Up%20Paddle/~rsqla/2010-Naish-Mana-10-0.aspx?search=uQNVTXNc1pVmLaT%2fQ5QGqg%3d%3dhttp://www.naishsurfing.com/en/boards/mana_2.htmlMalibu styled board.
This one looks like OK value....
www.seabreeze.com.au/Classifieds/Stand%20Up%20Paddle/~rspmf/2010-Molokai-Hawaii-11-0.aspx?search=uQNVTXNc1pVmLaT%2fQ5QGqg%3d%3dYou would love a DC16, DC17, or Naish17 for Murray Exploring too....
www.seabreeze.com.au/Classifieds/Stand%20Up%20Paddle/~r5luu/2010-Naish-Glide-17-0.aspx?search=uQNVTXNc1pVmLaT%2fQ5QGqg%3d%3dwww.naishsurfing.com/en/boards/glide_1.htmlwww.chapmansurfboards.com/stand-up-paddleboards/www.visithowlong.com.au/My recommendation would actually be a DC17, or Naish17, for river exploring. Whilst the S.I.C. F16 & 17 are also great boards, they are a little pricey, and probably have too much rocker for dedicated flatwater... ie, pushes water a touch, rather than slicing through it....
But these boards a not really an option for surfing, unless it is small waves, and no crowds.
Recommendation Number 2 - dive in the deep end, and get a board sooner rather than later!! You'll really enjoy it ! The longer you delay the purchase, the longer you delay enjoyment ! Great fitness too... someone said to me once, "no decision, is a decision (to do nothing)".
So many options.....

PS - the "borrow/hire/demo" option is probably going to be pretty damn difficult in Howlong !