I wouldn't be overly concerned about the tickets selling out soon, unless you're looking for cheap tickets to the semis / final. You can usually pick up tickets in most categories a week before the event, but obviously buy sooner if you want to pick better views.
Generally the best days to go are day 3 and 4, as the winners of the first two matches play (I.e best chance of seeing top 4 play each other in round robin stage), though you could equally get stuck watching the two losers. Last year the format changed so I think now day 3 and 4 are Wednesday and Thursday. Evening sessions don't start until 6, with doubles always first, so the singles match usually doesn't start until 8 or so. Unless your classes are in the evening then you could probably make these sessions. Easy to get to the o2 and easy to get home on the Tube.
The Saturday group stage matches (along with Friday) are the most likely to be dead rubbers between players already eliminated. If you want the best chance of competitive tennis go on Monday to Thursday, or the semis / final.
How many upper tier tickets are you buying for USD 150 / GBP 100? Sounds very expensive if it's just one. As long as the contract is still in place Ticketmaster is the sole primary agent, and Viagogo are the sole resale agent. See if you get the same prices through the official Barclay's WTFs site.
EDIT: I had a look at your link - don't buy from there. They are resale tickets with a face value of GBP 20 - 36 that they are selling for 100 to punters who don't know the face value of the tickets. Essentially they are touts buying pre-sale tickets and marking them up to rip tourists off who don't know how the system works.
The pre-sale ends tomorrow. If you want to buy tickets now you can use the code 45878867 on the official pre-sale site.
Or just wait a day. I doubt there'd be any more difficulty in getting the same seats. The primary distributor now seems to be axs.com; no idea if they are a subsidiary of Ticketmaster or whether it's a new partnership.
Ticket price range for group stages is GBP 20 - 65, so the resale tickets you were looking at were over 50% more than lower tier seats.