As far as squirrel proof feeder, lots of luck. In order to attract a wide variety of birds, you will want to provide a variety of seeds, not just sunflower. Costco and Sam's have premixed sacks that are wonderful, and a lot less expensive than the other stores. They come in 40 pound sacks and contain sunflower seeds, millet, peanuts, corn, etc. Stay away from milo, which most other mixed seed packages contain. Only doves eat it, and you don't want to attract them. They will eat you out of house and home, and bully the other birds away.
For birding try Mitchell Lake water treatment plant near San Antonio, and Warblerwoods in Cibolo, also near San Antonio.
I have an sx50 and really like it. the 530, if i am not mistaken, does not have a viewfinder, which makes it difficult to view your subject. You might check online for refurbs. The sx60 is the later model--not much difference, and more expensive.
The later you go in March the better, as migration will just be getting underway. Anywhere in the Rio Grande Valley should be good, depending on how early migration is. My favorites: Estero Llano Grande State Park, Bentsen Rio Grand State Park, Frontera,
Salineno,etc. Any of the parks in the Brownsville/Mcallen area. You might be interested in joining birdingpals/com. You can get in contact with local birders who are willing to take visitors around. If you get to central Texas, check out Warblerwoods. Where are you from?
i have used collage.com. good results. if you join groupon.com, they have specials all the time $40.00 books for 15.
Costco and Sam's club have great mixtures. no red milo. About $20.00 for 40 lb. sack. Attracts all kinds of birds.
You will need at least a 400mm to photograph birds and wildlife.
Just got back from south Florida. It was great for birds and wildlife.
The Harlingen/Weslaco/McAllen area of the Rio Grande Valley is excellent. My favorite park in Texas for bird watching and photography is Estero LLano Grande SP. The have guided walks most every day, led by Huck Hutchens. Also Laguna Atascosa Park, Bentsen Rio Grande Park, South Padre Island Convention Center, etc. All offer great photo ops. A good place to stay is the Alamo Inn in Alamo, near McAllen. It caters to birders. Keith, the owner is a photographer, and a fount of knowledge about birding the area. If you visit during the first week of November, you can sign up for the Rio Grande Valley Birding Festival. It is marvelous, and offers photo tours as some of its trips.
Good luck. You pretty much can't go wrong anywhere in the RGV.