Best way to connect Arista switches with QSFP+ ports with each other, and with SFP+ servers?

We have a mixture of Arista switches with QSFP+ ports, and servers with SFP+ ports:

• Arista 7050TX-64 - with 4 x QSFP+ ports
• Arista 7150S-64 - has 4 x QSFP+ ports
• Arista 7150S-24 - no QSFP+ ports, but has SFP+ ports
• Servers with Mellanox ConnectX-3 cards, and SFP+ optics (10GBASE-LR, SFP+, 1310nm)

We have bundles of OS2 duplex fiber optic cable running between the switches (although apparently I should have used multi-core MTP/MTO instead).

We have also bought LC-LC UPC Duplex OS2 patch leads.

For the QSFP+ ports - I have Mellanox QSFP+ to SFP+ adapters - however, according to here I should be using 40Gbps optics and breakouts instead.

My question is:

1. What's the best way of connecting up the switches (QSFP+ to QSFP+ and QSFP+ to SFP+)?
2. What's the best way of connecting up switches to servers? (i.e. which optic and breakout cables exactly should I be using?)

For example, I saw there's this optic for pretty cheap - however, it's 40GBASE-SR4. I assume it won't work with my existing 10GBASE-LR optics at the other end in servers? So should I be getting this optic instead? (Pretty big price increase).

Then for the breakout cable - is something like this breakout cable what I want?

Or if anybody knows a better way?

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