As FaTAir stated,
The solid Cu center conductor is probably not necessary for short cable runs.
I have a very long cable run to a motorized dish, approx 280 feet +. With standard Cu clad center conductor (RG-6 cable), I had trouble driving my motor with about 2/3 shorter cable run. I had a temporary cable run laid out just for testing which was a straight shot from the dish through my open front door and across the living room floor directly to my IRD. Not exactly what I desired for a long term installation! LOL The signal quality was fine, but the motor control was lacking. I also knew that I was going to have to add a lot more cable to lay it out properly. I opted for solid Cu center conductor RG-11 cable for my installation and have never had a motor control problem with that. I bought this as a bulk 1,000 foot roll and saved some $ / foot. Total price was more, obviously, but price per foot was equal to or less than a 50 or 100 foot roll of RG-6 from a hardware store.
Personally, since you already have the 76 cm dish, I wouldn't bother upgrading it right away to 90 cm, 1 M or 1.2 M. You may or may not find it to be necessary. After you have everything installed, do some investigation regarding the reception of the DVB-S2/8PSK signals using the 76 cm dish. If you cannot acquire them, then you will know that you truly need a larger dish and can decide what size to go for then.
I like the GeoSatpro 1.2 M dish because it is really well made and easy to install and align. I tried a 1M Winegard and I was not very pleased with it. It was extremely sensitive to the alignment. This is good for adjacent signal rejection, but it had to be so perfectly aligned that it was not very happy to be on a motor. Any minute slop in the motor backlash would not allow it to position properly.
With my Winegard DS-2076 dish, I was able to get OETA PBS on AMC 14 @ 125°W. This is a DVB-S2/8PSK signal. It may have been a stronger signal than other DVB-S2/8PSK signals on other sats, but I know that at least this channel worked.
Trees will definitely block the signal. Even small branches will. If there are leaves on these branches and especially if they are wet with rain or full of moisture from their roots, that will absorb the signal and prevent it from reaching your dish. However, keep in mind that often the satellites are MUCH higher in the sky than you think. If you are using an offset Ku band dish, the dish will actually be aiming higher than it really looks at first glance.
This is where the solar outage calculator
Sun Outage Calculator comes in very handy (one time in the spring and once in the fall). You can stand at the dish installation spot and look at the sun's position in the sky on the proper day and time of the solar alignment and see directly where the satellite is. If the sun is blocked by branches and leaves or a trunk of a tree, the satellite will be blocked, too.
When I was deciding where to locate my dish, I picked out several spots in the yard that made the most sense. i.e. Shortest distance to the house for the shortest cable run, out of the way from most of the lawn mowing and not so detracting from the look of the aesthetics. Also, not where I knew the snow to accumulate too deeply or the wind to blow too much. Then, during the solar outage dates and times, I checked the LOS view at each selected spot for every satellite. Well, I found the best location, but had to sacrifice a bit on the distance away from the house and the shelter from the wind to a certain extent. Never the less, I ended up with a full LOS for every satellite across my horizon. If the satellite is above the horizon limits, I can see it without any obstructions from trees or buildings or what not.
RADAR