Best setup for Studio One v3 on Surface Pro 4 for low latency and recording guitar

I am very new to all this stuff and really struggling with getting set up to enjoy latency free playing and recording. Can anyone recommend the best setup please?

Issues

When recording guitar there is a significant lag (fraction of a second, but that is enough to make playing complex melodies with a digital delay almost impossible).

If I have a couple of decent rich pads playing then I am getting CPU overload in a most distracting maer.

These are possibly two different problems, but I'd like to solve them both ideally :)

What I have tried

1. Installing asio4all
2. messing about with different variants of block size, etc. I just don't really know where I am hitting setup limitations or just being incompetent.

Setup

• Studio One Professional v3.5.1 x64
• Surface Pro 4 i7 2.2GHz with 16GB ram ruing Windows 10 Pro
• (asio4all latest version)
• Roland UA-25EX audio interface (which I have had for years so might be out of date)
• An electric guitar