1. The first part of your route appears to be the South Downs Way (SDW).
- check that you have got an accurate gpx for the route. I think it is very easy to make a mistake and go off course.
- it is a physically demanding route. Instead of staying on a ridge throughout, much of the route involves fairly steep ascents and descents. Much of the trail surface is chalk, which is likely to be slippery when wet, and there is a high risk of falling off your bike on the chalk surface descents if you do not ride with care.
- it is a route best suited to an MTB/VTT.
2. Probably the best source of information online about cycling the SDW is the Singletrackworld forum. If you search that forum, you should be able to find quite a few threads about forum member's SDW rides, and providing answers to questions about the route. You will probably find a link to a gpx in the threads, or if not join the forum and post a thread requesting one. This (long running) thread is the most recent, and includes photographs giving some idea of the terrain (but not the toughest hills and descents):
https://singletrackworld.com/forum/topi ... o-the-a31/
As in the thread above, most people ride the SDW from west to east, so you will be doing it in reverse to most people's accounts of their ride. Many people ride the route in one long day, but the poster in the thread above took longer and bivi'd.
3. I think you will need a ground mat and bivi bag (or bivi bag and tarp, or even an ultra-light tent) in addition to (or instead of) your hammock. I think you would find it difficult in some places to find a suitable spot with trees to use your hammock. If you ask on Singletrackworld they should be able to confirm whether a hammock is practical, but the photographs in the thread above make me think not.
4. There are several places along the SDW where there are potable water taps. It is likely to be essential to know where every one of them is, and to refill your bottles at each one, because it may be some distance to the next tap. Again, you could ask for advice on this point on Singletrackworld. It might be that the taps are marked on a gpx. The locations of taps are also shown on this map:
https://www.amazon.co.uk/South-Downs-XT ... 851374779/
See also
https://southdownsway.org
5. The SDW links up with the King Alfred's Way (KAW). I would not bother with your planned detour south of Winchester, and would instead carry on from the SDW on the KAW until you reach the Salisbury Plain. The KAW was developed by Cycling UK a couple of years ago using existing off-road rights of way. It is quite popular, partly because it is so new and has caught the attention of many off-road cyclists. Details here:
https://www.cyclinguk.org/route/king-al ... -gpx-route
If you search this forum you will find a number of threads about the KAW. I suggest you see this thread (especially videos in the post to which I have linked, and there are a couple of other videos later in the thread):
viewtopic.php?p=1524620#p1524620
See also
viewtopic.php?t=145613
6. As mentioned above,
https://bearbonesbikepacking.co.uk is likely to be a good source of information, and I would recommend joining the forum and asking for advice on your planned route (and whether a hammock is likely to be practical). They can probably give you good advice on your whole route.